Provide default values for tags for Micrometer

Release notes: The metrics-micrometer module's behaviour is changed to accommodate Micrometer issue 877. From core-io 2.4.10, SDK metrics were output in the following form, with the bucket, scope and/or collection tags added only to operations where they applied:

db.couchbase.operations{service="kv",db.name="bkt",db.couchbase.scope="scp",db.couchbase.collection="coll",outcome="success"}

db.couchbase.operations{service="query",outcome="success"}

However, this lead to Micrometer silently dropping some metrics due to the issue linked above. To avoid this, the SDK now outputs empty values for non-relevant tags, like so:

db.couchbase.operations{service="kv",db.name="bkt",db.couchbase.scope="scp",db.couchbase.collection="coll",outcome="success"}

db.couchbase.operations{service="query",db.name="",db.couchbase.scope="",db.couchbase.collection="",outcome="success"}

This change only affects the metrics-micrometer module. The metrics-opentelemetry module is unchanged.

See CBSE-17070