Convert security sidebar to a panel

What does this MR do and why?

This rewrites the instance-level Security sidebar using a panel instead of a custom HAML view. This makes it easier for us to support that sidebar in the upcoming super sidebar.

Screenshots or screen recordings

Nav	Before	After
Current nav
New nav	Same as above

How to set up and validate locally

1. Navigate to the instance security dashboard at /-/security/dashboard.
2. To enable the new nav:

   1. Enable the feature flag:

      echo "Feature.enable(:super_sidebar_nav)" | rails c

   2. Enable the user setting from the user dropdown:

      

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #391502 (closed)