Add prepared_stmt_count metrics to mysql integration

[keisku]

What does this PR do?

Add following metrics:

• mysql.performance.prepared_stmt_count
• mysql.performance.max_prepared_stmt_count

Motivation

mysql.performance.prepared_stmt_count is to get the current number of prepared statements.
https://dev.mysql.com/doc/refman/8.0/en/server-status-variables.html#statvar_Prepared_stmt_count

mysql.performance.prepared_stmt_count is to get the total number of prepared statements in the server.
https://dev.mysql.com/doc/refman/8.0/en/server-system-variables.html#sysvar_max_prepared_stmt_count

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

[justiniso]

Hey @kei6u thanks for the PR!

Overall, this looks good to me but I left a few suggested changes. I believe the metrics should be GAUGEs because they reflect the current state at the time of capture according to the documentation, but let me know if there was a reason you went with COUNTs. Thanks!

[keisku]

@justiniso
I appreciate your review!

let me know if there was a reason you went with COUNTs.

I set it as COUNT by getting from the name of metric(prepared stmt "count") since I actually was not sure how to decide a metric type. Now, I understand why I should've set it as GAUGEs.

[justiniso]

Thanks @kei6u, I went ahead and merged this. You can expect it to go out in agent version 7.35.0.