[JENKINS-69613] Reduce log output at INFO level

[MarkEWaite]

JENKINS-69613 - Reduce logging of polling and indexing events

Require a non-default logging level to see messages related to polling and indexing, including the "polling not triggered", "polling triggered", and "indexing triggered" messages.

Only changes the logging level, not the availability of those log messages.

Checklist

• I have read the CONTRIBUTING doc
• I have referenced the Jira issue related to my changes in one or more commit messages
• I have added tests that verify my changes
• Unit tests pass locally with my changes
• I have added documentation as necessary
• No Javadoc warnings were introduced with my changes
• No spotbugs warnings were introduced with my changes
• Documentation in README has been updated as necessary
• Online help has been added and reviewed for any new or modified fields
• I have interactively tested my changes
• Any dependent changes have been merged and published in upstream modules (like git-client-plugin)

Types of changes

• New feature (non-breaking change which adds functionality)