Add External Issue Tracker, Jira, and Labels menus

What does this MR do?

This MR moves the External Issue Tracker, Jira, and Labels menus from the HAML file to the new project sidebar refactor.

How to test the MR

In order to test this MR I recommend following steps:

• Go to Project > Settings > Integrations. Search for Custom issue tracker, fill all the data, and check Active. You should see the new menu
• Disable the Active field. You should no longer see the menu
• Go to Project > Settings > Integrations. Search for Jira. Fill all the details except for Enable Jira issues. You should see the same menu as with the Custom issue tracker.
• Now, check the Enable Jira issues field. You should see now the new Jira menu with two menu items.
• In order to test Labels we need to go to Project > Settings > General. There, we should look for Visibility, project features, permissions and set the toggle for Issues as disabled. Now you should see the Labels menu.

Screenshots (strongly suggested)

Before the MR	After the MR

With this refactor we're also fixing a bug in the Labels menu when the sidebar is collapsed. When we hover the Labels menu, with old code we get:

Nevertheless, now, when we hover after the MR, it looks like:

Does this MR meet the acceptance criteria?

Conformity

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

Related to #326428 (closed)