Add parseBoolean helper function

What does this MR do?

This introduces a new parseBoolean() helper function similar to parseInt().

We already had a helper with same functionality called convertPermissionToBoolean(). However that name was suggesting it only works for permissions. This merge request marks it deprecated and a future merge request will remove it completely.

What are the relevant issue numbers?

follow-up from https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/8519#note_118820779

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides
• Link to e2e tests MR added if this MR has Requires e2e tests label. See the Test Planning Process.