SMQ-3224 - Add consistent error for assigning channel and client with parent group to parent group

[felixgateru]

What type of PR is this?

This is a bug fix because it fixes the following issue: #3224

What does this do?

This pr add consistent error handling for assigning an already assigned channel and client to a parent group

Which issue(s) does this PR fix/relate to?

• Related Issue Bug: Assigning clients that already exist to a group doesn’t raise an error, but assigning channels that already exist does. #3224
• Resolves Bug: Assigning clients that already exist to a group doesn’t raise an error, but assigning channels that already exist does. #3224

Have you included tests for your changes?

Yes, tests have been updated.

Did you document any new/modified feature?

In code documentation is included

Notes

[codecov]

Codecov Report

❌ Patch coverage is 66.66667% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 34.42%. Comparing base (cac6c64) to head (122c29c).

Files with missing lines	Patch %	Lines
channels/service.go	60.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3225      +/-   ##
==========================================
- Coverage   35.54%   34.42%   -1.13%     
==========================================
  Files         307       68     -239     
  Lines       39233    14204   -25029     
==========================================
- Hits        13947     4890    -9057     
+ Misses      24439     9006   -15433     
+ Partials      847      308     -539     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.