fix: Do not enforce max_limits if inbox_auto_assignment is disabled (#11849)

# Pull Request Template

## Description

The `auto_assignment` max_limits were being enforced even if the inbox
level `auto_assign` feature was disabled. This was because the
enterprise method was not verifying the feature status before returning
the available agents.

## Type of change

Please delete options that are not relevant.

- [x] Bug fix (non-breaking change which fixes an issue)


## How Has This Been Tested?
- Tested locally
- Added Specs

## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [x] Any dependent changes have been merged and published in downstream
modules

enterprise/app/models/enterprise/inbox.rb

@@ -1,5 +1,7 @@
 module Enterprise::Inbox
   def member_ids_with_assignment_capacity
+    return super unless enable_auto_assignment?
+
     max_assignment_limit = auto_assignment_config['max_assignment_limit']
     overloaded_agent_ids = max_assignment_limit.present? ? get_agent_ids_over_assignment_limit(max_assignment_limit) : []
     super - overloaded_agent_ids