add sha256 fingerprint to SSH key view and api to query user by ssh fingerprint

What does this MR do?

This MR adds SH256 fingerprints to the SSH Key view, see also #15540 (closed)

update: and provides an API endpoint to search a user via API by providing a fingerprint(md5 or sha256), see: #24046

🔧 with ❤ at Siemens

Screenshots

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