fix: Discussions UI fixes on mobile resolutions

[Lunyachek]

This is backport from master PR - https://github.com/openedx/frontend-app-discussions/pull/689

Description

Fix user icon shrinkage

Before

After

Fix username overlapping with comment text, in cases when username is too long

Before

After

Added more space for long username by moving additional post data to the next row

Before

After

Fix sidebar width on tablet resolutions

On tablet resolutions, the sidebar becomes larger than on desktop. We believe this is illogical and fixed it

https://github.com/openedx/frontend-app-discussions/assets/19806032/3cacab34-76fa-454a-8911-43f68438860c

Before

After

Merge Checklist

• [ ] If your update includes visual changes, have they been reviewed by a designer? Send them a link to the Sandbox, if applicable.
• [ ] Is there adequate test coverage for your changes?

Post-merge Checklist

• [ ] Deploy the changes to prod after verifying on stage or ask @openedx/edx-infinity to do it.
• [ ] 🎉 🙌 Celebrate! Thanks for your contribution.

[openedx-webhooks]

Thanks for the pull request, @Lunyachek! Please note that it may take us up to several weeks or months to complete a review and merge your PR.

Feel free to add as much of the following information to the ticket as you can:

• supporting documentation
• Open edX discussion forum threads
• timeline information ("this must be merged by XX date", and why that is)
• partner information ("this is a course on edx.org")
• any other information that can help Product understand the context for the PR

All technical communication about the code itself will be done via the GitHub pull request interface. As a reminder, our process documentation is here.

Please let us know once your PR is ready for our review and all tests are green.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

:exclamation: No coverage uploaded for pull request base (open-release/quince.master@efa0c1c). Click here to learn what that means.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## open-release/quince.master #690 +/- ## ============================================================= Coverage ? 92.43% ============================================================= Files ? 169 Lines ? 3451 Branches ? 898 ============================================================= Hits ? 3190 Misses ? 241 Partials ? 20 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[openedx-webhooks]

@Lunyachek 🎉 Your pull request was merged! Please take a moment to answer a two question survey so we can improve your experience in the future.