feign-micrometer: No client tag on MicrometerObservation meters

[iCiaran]

When using the MicrometerObservationCapability (as autoconfigured by spring-cloud-openfeign) no information about the client is attached to the http.client.requests or http.client.requests.active meters.

This can be confusing for applications that have more than one feign client, especially when multiple clients have the same path template resulting in the metrics being merged.

For monitoring it would also useful to be able to filter metrics by client (different downstreams have different latency expected etc).