Stop query activity collection due to misconfiguration

[alexbarksdale]

What does this PR do?

Stops the collection of query activity if the database instance is not configured properly.

Motivation

If a specific config option isn’t enabled at the database level (performance-schema-consumer-events-waits-current), our collection query for activity does not error out, but rather collects data that is wrong or misleading.

Additional Notes

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[codecov]

Codecov Report

Merging #12343 (4e231fa) into master (d8a8f09) will increase coverage by 0.05%.
The diff coverage is 87.50%.

Flag	Coverage Δ
mysql	89.08% <87.50%> (+1.56%)	⬆️

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[justiniso]

This is a nit that is out of scope for this PR because the pattern already exists, but for the future I think it would be better to make this a boolean function and change the query to:

 cursor.execute(
                    """\
                    SELECT count(*)
                    FROM performance_schema.setup_consumers WHERE NAME = 'events_waits_current'
                    AND ENABLED = 'YES'
                    """
                )
return cursor.fetchone()[0] > 0

This would avoid leaking state and making the monolithic class more complex with additional public variables.