Support TiDB Dashboard

[djshow832]

Development Task

To support querying in dashboard, there are these things to do:

• Register TiProxy into PD #307
• api: add json format response #385 TiProxy supports /api/config interface to fetch config
• Provide log search service #313
• Provide system info and load service #314
• Support cluster_xxx(diagnostics service) for tiproxy tidb#47962 Add tiproxy for cluster_info tidb#47784 Support 6 cluster tables in information_schema on the TiDB side
• Dashboard fetches TiProxy topology from PD and checks its activity through TTL
• api: add grpc and diagnostics #388 Modify apiserver/clusterinfo and its UI
• api: add grpc and diagnostics #388 Modify apiserver/logsearch and its UI
• api: add grpc and diagnostics #388 Modify apiserver/conprof, ng-monitoring/confprof and its UI
• api: add grpc and diagnostics #388 Modify apiserver/profiling and its UI