Previously, Couchbase's health was determined by retrieving the bucket info
from the cluster info. This retrieval could take over one minute in some
cases even when Couchbase is health. This latency is too large for a health
check.

The Couchbase team have recommended the of a Cluster#diagnostics instead.
This provides a much lower latency view of the cluster's health. This
commit updates CouchbaseHealthIndicator to use Cluster#diagnostics while
retaining support, in a deprecated form, for the old info-based mechanism
should anyone want to opt back into that in 2.0.x.

Closes gh-14685