Fix #11357 - DB migration for custom metrics

[TeddyCr]

Describe your changes:

Fixes #11357

• rename profile metric key to customMetrics
• Delete customMetrics for extension. Implementation has been overhauled and OM has not had support for computing custom metrics since now. As a result we are deleting the existing data if any were ingested from via the API. Users we'll need to recreate it if there were some customMetrics definition

Type of change:

• Bug fix
• Improvement
• New feature
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation

Checklist:

• I have read the CONTRIBUTING document.
• My PR title is Fixes <issue-number>: <short explanation>
• I have commented on my code, particularly in hard-to-understand areas.
• For JSON Schema changes: I updated the migration scripts or explained why it is not needed.

• I have added tests around the new logic.
• For connector/ingestion changes: I updated the documentation.