Add GLQL ruby gem target

The gem was bootstrapped with

bundle gem --ext=rust glql_rb

Most of the files here were automatically generated. Main focus should be in

• glql_rb/ext/glql_rb/src/lib.rs
• glql_rb/spec/glql_rb_spec.rb
• glql_rb/Rakefile
• .gitlab-ci.yml

I've only added jobs to build and test the ruby gem for now.

I took inspiration from https://gitlab.com/gitlab-org/ruby/gems/gitlab-glfm-markdown, but I didn't add support yet for the items below, which I'm planning to do on a separate iteration as I wanted to get this first iteration reviewed first.

• crossplatform builds ( supported in the rakefile, but didn't add a job for it )
• multiple versions of Ruby. Not sure if this is needed?
• gem publishing

I'm no expert of Ruby gem building ( and related CI jobs ), so would def need a review from an domain expert.

Related to https://gitlab.com/gitlab-org/gitlab/-/issues/573055