[FEATURE] Add Luxembourgish (lb) as supported language

Luxembourgish is considered the national language of
Luxembourg and one of the three used administrative
languages, alongside German and French.

Also see https://en.wikipedia.org/wiki/Luxembourgish

This change adds support for Luxembourgish to be selected
as TYPO3 Language and to connect to TYPO3 Localizations
(XLF files, Site Configuration) by default.

Resolves: #97254
Releases: main
Change-Id: I334c1d9c00d941754f23c6a82412702796c94339
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/74119


Tested-by: core-ci <typo3@b13.com>
Tested-by: Chris Müller <typo3@krue.ml>
Tested-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Chris Müller <typo3@krue.ml>
Reviewed-by: Oliver Bartsch <bo@cedev.de>