Add Merge Requests and Requirements Menu

What does this MR do?

This MR moves the Merge Requests and Requirements menus from the HAML file to the new project sidebar refactor.

Screenshots (strongly suggested)

Before the MR	After the MR

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have not included a changelog entry because it's a tooling change.
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Related to #326429 (closed)