Moved cleanup activities logic to activity bounded context. (#40663)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #38536 

Split the activities cleanup job from the queries cleanup job.

# Checklist for submitter

- [ ] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
  - Present in previous PR

## Testing

- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

## Release Notes

* **New Features**
* Added automated cleanup job for expired live queries based on activity
expiration settings.

* **Improvements**
* Refactored activity data cleanup to use a dedicated service for better
reliability and maintainability.
* Enhanced scheduled cleanup operations with improved separation of
concerns for activity and live query management.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

server/activity/api/cleanup_expired_activities.go

@@ -0,0 +1,11 @@
+package api
+
+import "context"
+
+// CleanupExpiredActivitiesService cleans up expired activities.
+type CleanupExpiredActivitiesService interface {
+	// CleanupExpiredActivities deletes up to maxCount activities older than expiryWindowDays
+	// that are not linked to any host. Host-linked activities are preserved
+	// (they are cleaned up when the host activity is processed).
+	CleanupExpiredActivities(ctx context.Context, maxCount int, expiryWindowDays int) error
+}

server/activity/api/service.go

@@ -9,4 +9,5 @@ type Service interface {
 	ListHostPastActivitiesService
 	StreamActivitiesService
 	NewActivityService
+	CleanupExpiredActivitiesService
 }