Rename gem from releases to gitlab-releases

This renames the gem from releases to gitlab-releases, bumping to version 0.2.0.

See https://gitlab.com/gitlab-org/delivery/releases/-/merge_requests/6/diffs for a similar MR that recently renamed the gem for comparison.

Related to gitlab-com/gl-infra/delivery#19597 (closed)

Testing

~/workspace/gitlab-org/gitlab-releases (rename-gem-to-gitlab-releases ✔) gem build gitlab-releases.gemspec --debug
NOTE:  Debugging mode prints all exceptions even when rescued
  Successfully built RubyGem
  Name: gitlab-releases
  Version: 0.2.0
  File: gitlab-releases-0.2.0.gem
~/workspace/gitlab-org/gitlab-releases (rename-gem-to-gitlab-releases ✗) gem install gitlab-releases
Successfully installed gitlab-releases-0.2.0
Parsing documentation for gitlab-releases-0.2.0
Installing ri documentation for gitlab-releases-0.2.0
Done installing documentation for gitlab-releases after 0 seconds
1 gem installed
~/workspace/gitlab-org/gitlab-releases (rename-gem-to-gitlab-releases ✗) PRODUCTION_TOKEN=<REDACTED> irb
irb(main):001:0> require 'gitlab_releases'
=> true
irb(main):002:0> GitlabReleases.upcoming_releases
=>
{"16.3"=>"2023-08-22",
 "16.4"=>"2023-09-22",
 "16.5"=>"2023-10-22",
 "16.6"=>"2023-11-16",
 "16.7"=>"2023-12-21",
 "16.8"=>"2024-01-18",
 "16.9"=>"2024-02-15",
 "16.10"=>"2024-03-21",
 "16.11"=>"2024-04-18",
 "17.0"=>"2024-05-16",
 "17.1"=>"2024-06-20",
 "17.2"=>"2024-07-18",
 "17.3"=>"2024-08-15"}
irb(main):003:0> GitlabReleases.active_version
=> "16.4"
irb(main):004:0> GitlabReleases.current_version
=> "16.3"
irb(main):005:0> GitlabReleases.next_versions
=> ["16.3.1", "16.2.5", "16.1.5"]