Add selecting tags on the compare page (#15723)

* Add selecting tags on the compare page

* Remove unused condition and change indentation

* Fix tag tab in dropdown to be black

* Add compare tag integration test

Co-authored-by: Jonathan Tran <jon@allspice.io>

options/locale/locale_en-US.ini

@@ -1286,6 +1286,9 @@ issues.review.resolved_by = marked this conversation as resolved
 issues.assignee.error = Not all assignees was added due to an unexpected error.
 issues.reference_issue.body = Body
 
+compare.compare_base = base
+compare.compare_head = compare
+
 pulls.desc = Enable pull requests and code reviews.
 pulls.new = New Pull Request
 pulls.compare_changes = New Pull Request