Invenio-i18n

- add method to check if locale is available

- Remove deprecated flask-babelex
- Expose LazyString, gettext from flask_babel to invenio
- Fix get_locale in cli (without request context)
- Replace set_locale with flask_babel.set_locale
- Use Multidomain translation in flask_babel context

- Adds translations
- Updates invenio dependencies
- refactors CI tests

- Adds support for Flask v2.1

- Fixes issue with language selector button not disabling the currently
selected field.

- Integrates Semantic-UI templates and assets.
- Removes webassets-based bundles.
- Adds InvenioI18N extransion to the API level applications.