Create a build-infos.json file containing firefox platform_version and buildid

To generate the update-responses xml, we need to know the firefox platformVersion and buildID.

In standard releases we generate a config.yml from projects/release/update_responses_config.yml which includes the platformVersion it gets from the rbm config. To get the buildID the update_responses script will extract a mar file to get it from application.ini.

While generating updates-responses xml for nightly builds (in #25102 (moved)), we don't have easy access to the platformVersion. I think we could add it in a build-infos.json file. At the same time we can also include the buildID in that same file which removes the need to have mar-tools available to extract a mar file.