Submit database_hostname with database_instance

[sethsamuel]

What does this PR do?

Adds database_hostname (reflecting the actual host of the database for MySQL, Postgres, and SQLServer) to database instance metadata and server metrics.

Motivation

We currently submit reported_hostname as host and database_instance but this prevents users from grouping metrics by the underlying host. With database_hostname users will be able to do so even when using reported_hostname as a way of differentiating multiple database instances on a single host.

This is a purely additive change that does not yet tackle the full database instance/host problem.

See this ticket
for an example of a customer unable to correlate DBM metrics with infrastructure metrics.

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Add the qa/skip-qa label if the PR doesn't need to be tested during QA.
• If you need to backport this PR to another branch, you can add the backport/<branch-name> label to the PR and it will automatically open a backport PR once this one is merged

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.34%. Comparing base (7b18212) to head (8a71460).
Report is 29 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
activemq	?
cassandra	?
hive	?
hivemq	?
hudi	?
ignite	?
jboss_wildfly	?
kafka	?
mysql	89.55% <100.00%> (+0.01%)	⬆️
postgres	93.27% <100.00%> (+3.95%)	⬆️
presto	?
slurm	?
solr	?
sqlserver	91.14% <100.00%> (+9.24%)	⬆️

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