Move ConvDev Index location to after Cohorts

What does this MR do?

Moves the ConvDev tab from the Monitoring menu to the Overview menu.

Screenshots (if relevant)

Before:

After:

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• All builds are passing
• Has been reviewed by Frontend

What are the relevant issue numbers?

Closes #34413 (closed)

EE Compatible MR: https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2732