Resolve "Credentials inventory for group managed accounts"

What does this MR do?

Resolves #38133 (closed)

We currently have Credentials inventory at the Instance level: #36742 (closed)

With #38133 (closed), we are trying to build this at the Group level too, for groups that supports managed accounts.

Access Policy

• credentials_inventory feature should be enabled - this is GitLab Ultimate only
• The accessing user should be admin of the instance or owner of the group. Feature is not available to maintainers, developers etc.
• The group should enforce group managed accounts. This feature is not available for normal groups.

Screenshots

Personal Access Tokens:

SSH Keys:

Sidebar:

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #38133 (closed)