Update Visual Review Toolbar to post to MRs

What does this MR do?

The first version of this (gitlab-ce!27518 | !11605 (merged)) is posting to issues instead of merge requests. This fixes that. 🙈

The form can be tested at https://review-app-test.sarahghp.now.sh/ and posts to sarahghp/review-app-tester!1.

Does this MR meet the acceptance criteria?

Conformity

• Code review guidelines
• Style guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.