[DBMON-5793] Fix mysql explain plan error reporting

[eric-weaver]

What does this PR do?

The goal of this change is to cleanup errors captured on explain plan events so that they are more clear for users. We now capture exception messages properly. When the error explaining is due to a permission error or missing explain procedure we'll now have a unique error marker which will allow us to surface a clearer message in the DBM UI. We'll still fallback to the old explain plan error view for connection or other errors

Currently explain plan errors will show like this

After this change it will look like this

Motivation

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 89.12%. Comparing base (497be69) to head (57a0b00).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

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Review from sethsamuel is dismissed. Related teams and files:

• database-monitoring-agent
  • mysql/changelog.d/21693.fixed