Add GitLab::Utils.to_exclusive_sentence

What does this MR do?

Adds a new GitLab::Utils.to_exclusive_sentence which wraps ActiveSupport's Array#to_sentence to convert the given array to a comma-separated sentence joined with localized 'or' Strings instead of 'and'. Refactors the existing code to use the new method.

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• [-] Tested in all supported browsers