HEC client metrics

[rquinio1A]

Some metrics linked to the HEC client (HTTP connection pool, number of events batch ok/failed, etc.) would be interesting for monitoring purposes.

[vietk]

Actually there's ok http3 binder for micrometer : https://github.com/micrometer-metrics/micrometer/tree/main/micrometer-core/src/main/java/io/micrometer/core/instrument/binder/okhttp3