Credential inventory for group managed accounts

Problem

We explored the need for a credential inventory in #32463 (closed), and have an MVC represented in #36742 (closed).

This MVC covers self-managed GitLab instance, but does not provide oversight for customers using GitLab.com. For these organizations, we need to consider executing this at the group-level.

Proposal

Introduce an credential inventory for group managed accounts mapped to the group. A group Owner should be able to see PATs and SSH keys for managed users with the same information for each credential that we expose in #36742 (closed).

Group-level Security View
A Credentials page within the Group's Security menu item that lists PATs and SSH keys based on #36742 (closed)

Permissions

Only Group Owners should be able to view this page.

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