refactor: change lang selector logic

[dcoa]

Description and motivation

This PR refactors the lang selector logic recognizing its significance for multi-language instances.
The Open edX platform previously featured a configurable language selector in both the header and footer. However, after transitioning to microfrontends, this feature is only partially implemented in the footer. It requires passing a list of supported languages and a change function, necessitating additional modifications even when using the footer slot.

This PR change the dropdown and add the user preference update endpoint.

Proposal

Convert this component in a slot so could be installed in the header as well and give them the operators the option to use the language selector in the header or footer.

How to test

1. Override the Footer component in a MFE or use the example application to test the current implementation.
2. Add the configurations via env,config.js or MFE Config API.

const config = { ENABLE_FOOTER_LANG_SELECTOR: true, SITE_SUPPORTED_LANGUAGES: ['es', 'en'], };

3. You need the messages for the selected language if you want to visualize the change.
4. You can see the change in the language cookie.

2025-01-13.21-07-20.mov

[openedx-webhooks]

Thanks for the pull request, @dcoa!

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.25%. Comparing base (6e2ccf2) to head (3845c7f).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #493      +/-   ##
==========================================
+ Coverage   91.22%   94.25%   +3.02%     
==========================================
  Files           5        6       +1     
  Lines          57       87      +30     
  Branches       19       23       +4     
==========================================
+ Hits           52       82      +30     
  Misses          5        5              

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