Consider adding some gecko .ftl files to branding packages

[fabricedesre]

We see these l10n resource trying to be fetched from the branding package:

2022-10-28T08:46:39Z INFO  actix_web::middleware::logger "GET /locales/en-US/branding/brand.ftl HTTP/1.1" branding.localhost:8081 404 0 0.149000
2022-10-28T08:46:39Z INFO  actix_web::middleware::logger "GET /locales/en-US/dom/media.ftl HTTP/1.1" branding.localhost:8081 404 0 0.114000

They are in gecko, but we could customize them on the nutria side easily.