Even more xml docs + small changes

[marcinbudny]

Description

• XML docs for OpenTelemetry and Persistence
• ActivitySetup in OpenTelemetry now doesn't have to deal with null activities
• Parameter renamed in Persistence to be more consistent actorName -> actorId

Purpose

This pull request is a:

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)