Update gitlab-releases gem and rename dependencies

What does this MR do and why?

The releases gem was renamed to gitlab-releases. In this MR, we update the name, moving to version 0.2.0. Since the name changes, we also have updated our related client class to match.

An additional change is the gem is the PRODUCTION_TOKEN variable was renamed. This is reflected in the README. The new token RELEASES_GITLAB_READ_TOKEN has been added to release/tools on the ops instance, so this gem update will work once merged.

Related to gitlab-com/gl-infra/delivery#19594 (closed) and gitlab-com/gl-infra/delivery#19597 (closed)

Testing

~/workspace/gitlab-org/release-tools (delivery19594-rename-var ✔) RELEASES_GITLAB_READ_TOKEN=<REDACTED> be pry --gem
[1] pry(main)> ReleaseTools::GitlabReleasesClient.active_version
=> "16.4"
[2] pry(main)> ReleaseTools::GitlabReleasesClient.version_for_date(Date.parse('2023-12-14'))
=> "16.7"
[3] pry(main)> ReleaseTools::GitlabReleasesClient.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"}

Author Check-list

• Has documentation been updated?