Consolidate namespace provisioning syncs to use SyncRequestService

Background

This issue was created as a follow-up from the discussion in #12345 (comment 3076276299).

Currently, namespace provisioning syncs happen through multiple pathways, leading to inconsistency and reduced control over the sync process. This fragmentation makes it difficult to:

• Detect and track namespace syncs triggered from CDot
• Apply consistent controls (e.g., EligibilityService checks)
• Maintain a unified approach to provisioning workflows

Proposal

Consolidate all namespace provisioning sync pathways to go through the SyncRequestService. This includes:

1. Audit existing sync pathways - Identify all the different ways namespace syncs are currently triggered
   1. For instance, direct sync via AdminPanel done by Support
2. Use UpdatePlanInfoService - Ensure actions go through the usual provision workflows where possible
3. As UpdatePlanInfoService is dependent on order or trial object, so it may not be possible for Internal Namespace provision which doesn't have order. For those:
   1. Migrate to SyncRequestService - Update all sync operations to use SyncRequestService for capturing each namespace sync triggered from CDot
4. Apply consistent controls - Leverage existing controls like EligibilityService across all sync operations

Benefits

• Single source of truth for namespace sync operations
• Better observability and tracking of sync requests
• Consistent application of eligibility checks and other controls
• Easier maintenance and debugging
• Reduced complexity by eliminating "100 ways" of doing the same thing