DRY up "#{Gitlab.config.gitlab.host}:#{Gitlab.config.gitlab.port}" [RUN ALL RSPEC] [RUN AS-IF-FOSS]

What does this MR do?

As suggested by @tkuah, this MR replaces the multiple occurrences of "#{Gitlab.config.gitlab.host}:#{Gitlab.config.gitlab.port}" with a simple Gitlab.host_port, following the naming convention already used (eg. Gitlab.config.registry.host_port).

Closes #322521 (closed)

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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  • I have not included a changelog entry because this is a trivial change and is invisible to end-users.
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• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
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