BE: Connect custom status to all abstraction methods

• 1. Handle returning either system-defined or custom status, depending on whether custom statuses are enabled for the namespace by updating the following classes:
  • CurrentStatus
  • StatusBulkResolver for returning status lists
  • AllowedStatusesResolver for returning allowed statuses per work item type
• 4. Allow moving and cloning work items with a custom status. If a custom status doesn't exist in the target namespace, transition to the default open/closed/duplicated status instead - moved to a separate issue: BE: Allow moving and cloning work items with a ... (#547082 - closed).
• 5. Allow filtering by custom statuses by updating WorkItems::Widgets::Filters::Status as per this todo - will be updated via BE: Migrate system-defined statuses to custom s... (#524131 - closed).
• 6. Allow setting and updating status when a custom status value is provided by updating WorkItems::Callbacks::Status. - Already updated via Ensure consistency between states and correspon... (!191528 - merged).

Based on POC Draft: POC Static default status for work items (!178180 - closed)