Fix missing served_by_guid in boost partners #4878

Ticket(s) / Related Merge Requests

(Any issue cards for the merge request, and related merge requests/dependencies)

Summary of Changes

• adds a separate boosted content service for the channel feed
• adds served_by_guid to all entity metadata snowplow context

(Summarize the changes made concisely)

• Changelog file updated with this template (one or more)
  • Added for new features.
  • Changed for changes in existing functionality.
  • Deprecated for soon-to-be removed features.
  • Removed for now removed features.
  • Fixed for any bug fixes.
  • Security in case of vulnerabilities.

Testing Considerations

• make sure changing "boosts on my channel" settings to safe/controversial actually takes effect

Regression Scope

• channel feed

Platform Affected (web, mobile, etc)

(Which platforms are affected by this change? Web, Mobile, or Both?)

Developer Testing Completed

(What has been tested already?)

Screenshots

(Any extra UI screens that can be shared)

Does this impact

• Localization
• Dark/light mode
• Guest mode