Instance request endpoint should create true TLRs when feature is enabled

/circulation/requests/instances should create true TLRs when TLR feature is enabled.
Previously, it selected an item and created item-level requests. This logic should stay intact for cases when TLR feature is disabled. When it is enabled, true TLR needs to be created.
Scenario 1.

• Given: TLR feature is disabled
• When: call /circulation/requests/instances endpoint
• Then: item-level request should be created
  Scenario 2.
• Given: TLR feature is enabled
• When: call /circulation/requests/instances endpoint
• Then: title-level request should be created