feat: add language selector component to header

[andrey-canon]

Description

This is a backport of openedx#586
Issue # 1305

How to test

1. Checkout the required branches frontend-component-header and frontend-platform
2. Set both dependencies as editable in your MFE,e.g

module.exports = {
    /*
    Modules you want to use from local source code.  Adding a module here means that when this app
    runs its build, it'll resolve the source from peer directories of this app.
  
    moduleName: the name you use to import code from the module.
    dir: The relative path to the module's source code.
    dist: The sub-directory of the source code where it puts its build artifact.  Often "dist".
    */
    localModules: [
        { moduleName: '@edx/frontend-platform', dir: '../frontend-platform', dist: 'src' },
        { moduleName: '@edx/frontend-component-header/dist', dir: '../frontend-component-header', dist: 'src' },
        { moduleName: '@edx/frontend-component-header', dir: '../frontend-component-header', dist: 'src' },
    ],
};

3. Add the following settings to your local environment

MFE_CONFIG["SITE_SUPPORTED_LANGUAGES"] = ["en", "ar"]
MFE_CONFIG["ENABLE_HEADER_LANG_SELECTOR"] = True

4. Download you MFE messages
   export PATH="$(pwd)/node_modules/.bin:$PATH"
make OPENEDX_ATLAS_PULL=true ATLAS_OPTIONS="--repository=nelc/futurex-translations --revision=open-release/redwood.master" pull_translation
5. Go to your mfe an check the language selector behavior

2025-10-07.12-16-55.mp4

[johanseto]

LGTM
Working in my proto teak env

Screencast.from.08-10-25.10.54.39.webm

[johanseto]

As a reminder, please update or assist with this PR regarding the tests.
openedx#586