Correct the ordering of metrics on performance dashboard

What does this MR do?

Order metrics correctly on the performance dashboard.

When common metrics were moved from a yml file to the DB, the priority values were not added to the DB. In this MR, a priority column is added to the prometheus_metrics table and groups of common_metrics are ordered in descending order of priority. All metrics in a group are expected to have the same priority.

Custom metrics do not have a priority and will default to priority 0, as before.

What are the relevant issue numbers?

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.
• Security reports checked/validated by reviewer

Closes #51970 (closed)