[mongo] always emit database_instance

[lu-zhengda]

What does this PR do?

Always emit database_instance metadata regardless of dbm status.

Motivation

Additional Notes

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• Changelog entries must be created for modifications to shipped code
• 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 87.06%. Comparing base (c1e8530) to head (f8eedc2).
Report is 6 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
activemq	?
cassandra	?
hive	?
hivemq	?
hudi	?
ignite	?
jboss_wildfly	?
kafka	?
mongo	93.26% <100.00%> (-0.26%)	⬇️
presto	?
solr	?

Flags with carried forward coverage won't be shown. Click here to find out more.