Add schema tag to db_fragmentation metrics for sqlserver

[azhou-datadog]

What does this PR do?

A follow up to #19266. It is also very convenient to have the schema tag attached to db fragmentation metrics for sqlserver as well.

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 88.00%. Comparing base (ac01180) to head (83fc67b).
Report is 2 commits behind head on master.

Additional details and impacted files

Flag	Coverage Δ
activemq	?
cassandra	?
hive	?
hivemq	?
hudi	?
ignite	?
jboss_wildfly	?
kafka	?
presto	?
solr	?
sqlserver	91.15% <100.00%> (+9.50%)	⬆️

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