Restored removed self-assign articles to the pool of Available Articles

[omChauhanDev]

What this PR does

Fixes #5549 This pr helps in restoring the un-assigned article back to the pool of available articles.

Created action to unclaim the assignment. Created controller and its route in backend.

Videos

Before:

https://github.com/WikiEducationFoundation/WikiEduDashboard/assets/119471995/fa84e3b5-5e9d-4329-a49d-9412e3a68f09

After:

https://github.com/WikiEducationFoundation/WikiEduDashboard/assets/119471995/4ea3dd52-8518-4a51-8460-4cb80843a51d

[ragesoss]

@om-chauhan1 thanks! can you resolve the merge conflict?

[omChauhanDev]

@ragesoss i have resolved that merge conflict.

[omChauhanDev]

Failed test is passing locally.

[omChauhanDev]

@ragesoss Sir, kindly review this.

[ragesoss]

Sorry that it's taken me so long to have a look at this.

I took a look through the code and realized that there are some important details missing from the issue description. I'll add a comment on the issue to explain.