meshreg: add metrics

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添加 meshreg 指标：

• slime_meshregistry_enabled_source： 当前启用的注册中心总数
• slime_meshregistry_mcp_push_count：当前实例向 istiod 推送的次数
• slime_meshregistry_ready_time：启用的注册中心 source 达到就绪状态的耗时
• slime_meshregistry_polling_time：轮训模式从注册中心完成一次全量服务数据同步的耗时分布，分注册中心
• slime_meshregistry_polling_count：轮训模式向注册中心执行的全量服务数据同步的次数，分注册中心
• slime_meshregistry_service_entry_{creation,deletion,update}：执行 se 创建、删除、更新的次数，分注册中心
• slime_meshregistry_service_entry_total：当前内存中保存的 se 的总数
• slime_meshregistry_sidecar_{creation,deletion,update}：执行 sidecar 创建、删除、更新的次数，分注册中心
• slime_meshregistry_sidecar_total：当前内存中保存的 sidecar 的总数
• slime_meshregistry_source_event_count：注册中心 source 产生的配置变更事件的次数，分注册中心、配置类型、事件类型
• slime_meshregistry_source_client_request_count：向注册中心发起的请求的次数，分注册中心

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example:

# HELP slime_framework_submodules_count total number of submodules
# TYPE slime_framework_submodules_count gauge
slime_framework_submodules_count 1
# HELP slime_meshregistry_enabled_source Number of enabled sources.
# TYPE slime_meshregistry_enabled_source gauge
slime_meshregistry_enabled_source 3
# HELP slime_meshregistry_mcp_push_count Number of mcp push.
# TYPE slime_meshregistry_mcp_push_count counter
slime_meshregistry_mcp_push_count 1
# HELP slime_meshregistry_polling_time Time spent on polling in seconds
# TYPE slime_meshregistry_polling_time histogram
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="0.5"} 54
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="1"} 54
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="3"} 54
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="5"} 54
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="8"} 54
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="10"} 54
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="20"} 54
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="30"} 54
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="60"} 54
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="90"} 54
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="120"} 54
slime_meshregistry_polling_time_bucket{source="eureka",status="true",le="+Inf"} 54
slime_meshregistry_polling_time_sum{source="eureka",status="true"} 0.4265233670000001
slime_meshregistry_polling_time_count{source="eureka",status="true"} 54
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="0.5"} 27
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="1"} 27
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="3"} 27
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="5"} 27
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="8"} 27
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="10"} 27
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="20"} 27
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="30"} 27
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="60"} 27
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="90"} 27
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="120"} 27
slime_meshregistry_polling_time_bucket{source="nacos",status="true",le="+Inf"} 27
slime_meshregistry_polling_time_sum{source="nacos",status="true"} 2.307905504
slime_meshregistry_polling_time_count{source="nacos",status="true"} 27
# HELP slime_meshregistry_pollings_count Number of pollings by source.
# TYPE slime_meshregistry_pollings_count counter
slime_meshregistry_pollings_count{source="eureka",status="true"} 54
slime_meshregistry_pollings_count{source="nacos",status="true"} 27
# HELP slime_meshregistry_ready_time_seconds Time spent on ready in seconds
# TYPE slime_meshregistry_ready_time_seconds gauge
slime_meshregistry_ready_time_seconds{source="eureka"} 20.022335849
slime_meshregistry_ready_time_seconds{source="nacos"} 35.110287551
slime_meshregistry_ready_time_seconds{source="sources"} 36.025003446
slime_meshregistry_ready_time_seconds{source="zookeeper"} 1.521635244
# HELP slime_meshregistry_service_entry_creation Number of service entries created by source.
# TYPE slime_meshregistry_service_entry_creation counter
slime_meshregistry_service_entry_creation{source="eureka"} 5
slime_meshregistry_service_entry_creation{source="nacos"} 11
slime_meshregistry_service_entry_creation{source="zookeeper"} 12
# HELP slime_meshregistry_service_entry_total Number of service entries in the mesh registry by source.
# TYPE slime_meshregistry_service_entry_total counter
slime_meshregistry_service_entry_total{source="eureka"} 5
slime_meshregistry_service_entry_total{source="nacos"} 11
slime_meshregistry_service_entry_total{source="zookeeper"} 12
# HELP slime_meshregistry_sidecar_creation Number of sidecars created by source.
# TYPE slime_meshregistry_sidecar_creation counter
slime_meshregistry_sidecar_creation{source="zookeeper"} 6
# HELP slime_meshregistry_sidecar_total Number of sidecars in the mesh registry by source.
# TYPE slime_meshregistry_sidecar_total gauge
slime_meshregistry_sidecar_total{source="zookeeper"} 1
# HELP slime_meshregistry_source_client_request_count client request count by source, with status.
# TYPE slime_meshregistry_source_client_request_count counter
slime_meshregistry_source_client_request_count{source="eureka",status="true"} 54
slime_meshregistry_source_client_request_count{source="nacos",status="true"} 324
slime_meshregistry_source_client_request_count{source="zookeeper",status="true"} 25
# HELP slime_meshregistry_source_event_count config event count by source, with event type and config type, and status.
# TYPE slime_meshregistry_source_event_count counter
slime_meshregistry_source_event_count{config_type="networking.istio.io/v1alpha3/ServiceEntry",event_type="Added",source="eureka",status="true"} 5
slime_meshregistry_source_event_count{config_type="networking.istio.io/v1alpha3/ServiceEntry",event_type="Added",source="nacos",status="true"} 11
slime_meshregistry_source_event_count{config_type="networking.istio.io/v1alpha3/ServiceEntry",event_type="Added",source="zookeeper",status="true"} 12
slime_meshregistry_source_event_count{config_type="networking.istio.io/v1alpha3/Sidecar",event_type="Added",source="zookeeper",status="true"} 6