EventHubs metrics

[lmolkova]

Implements EventHub part of #25605

Adds following metrics to eventhubs (and blob checkpoint store)

Name	Description	Units	Instrument Type (*)	Value Type	Attribute Key(s)	Attribute Values
messaging.eventhubs.events.sent	Number of events sent	{events}	Counter	Long	net.peer.name	Broker FQDN
					messaging.destination (will change)	Entity name
					messaging.eventhubs.partition_id	Partition id (if known at send time)
					otel.status_code	ok or error
messaging.eventhubs.consumer.lag	Approximate lag between the time message was received and the time it was enqueued on broker.	seconds	Histogram	Double	net.peer.name	Broker FQDN
					messaging.destination	Entity name
					messaging.eventhubs.partition_id	Partition id
					messaging.eventhubs.consumer_group	Consumer group
messaging.eventhubs.checkpoints	Number of checkpoint update calls	{calls}	Counter	Long	net.peer.name	Broker FQDN
					messaging.destination (will change)	Entity name
					messaging.eventhubs.consumer_group	Consumer group name
					messaging.eventhubs.partition_id	Partition id
					otel.status_code	ok or error
messaging.eventhubs.checkpoint.sequence_number	Last checkpointed sequence number	{seqNo}	Gauge	Long	net.peer.name	Broker FQDN
					messaging.destination (will change)	Entity name
					messaging.eventhubs.partition_id	Partition id
					messaging.eventhubs.consumer_group	Consumer group name
					otel.status_code	ok or error

[azure-sdk]

API change check

APIView has identified API level changes in this PR and created following API reviews.

azure-messaging-eventhubs
azure-messaging-eventhubs-checkpointstore-blob

[conniey]

LGTM. Thanks!

[anuchandy]

thanks @lmolkova, LGTM.