[BACKPORT] fix: posts sorting on sidebar

[dyudyunov]

Backport from the master

Description

Fix wrong sorting when a user creates several posts without the page reloading.

Steps to reproduce

1. [Precondition] The new discussions experience (discussions sidebar) should be enabled
2. Navigate to any course unit where the discussions sidebar is enabled
3. Create a new post.
4. Click on the "Back to list" button. Note that the default sorting is used (most recent first) and it's correct.
5. Create another post without reloading the page
6. Click on the "Back to list" button and check the result

Actual result

The second created post is the last in the list (the same for any number of posts created additionally).

Expected result (with the fix applied)

Sorting works as expected - most recent posts are displayed first.

Additional Notes

• Reproduces only with the discussions sidebar inside the Learning MFE.
  That's because when you create a post in the Discussions MFE itself - you will be navigated to the "My Posts" tab and the list of the posts will always be fetched.
• Sorting works as expected after the page is reloaded.

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[dyudyunov]

My changes require further improvements - there are unneeded additional GET requests to the threads endpoint.

I will change the status to Draft for now

[dyudyunov]

My changes require further improvements - there are unneeded additional GET requests to the threads endpoint.

I will change the status to Draft for now

I figured out how to get rid of the unneeded API call, now it's ready for review