Add Rubygem platforms for GOV.UK environments
Add Rubygem platforms for GOV.UK environments

This adds Linux, Arm Linux and Arm MacOS platforms for bundler and
allows precompiled gems to be installed. This allows faster installation
on these platforms and resolves an issue on production where Rubygems can
get confused as to which gem to use [1]

[1]: https://github.com/alphagov/publisher/pull/1699/commits/cee149a469376ec9f3ef1577e207de285101783b

alphagov/content-tagger,alphagov/content-tagger,alphagov/content-tagger