Move profiles/keys#get_keys to users#ssh_keys on Web UI

What does this MR do?

Moves profiles/keys#get_keys to users#ssh_keys by moving get_keys action in profiles/keys_controller to users_controller with renaming as ssh_keys to get easier to distinguish it from "gpg_keys".

Note that this MR does not change routing.

Why?

As the API for List SSH keys for user has /users/:id_or_username/keys, we should align this Web UI endpoint with the counterpart API endpoint.

Why not profiles/keys#create?

That sounds a good catch 😁

Screenshots

n/a

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [n/a] Documentation (if required)
• Code review guidelines
• [n/a] Merge request performance guidelines
• Style guides
• [n/a] 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
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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:

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