Automatic merge from submit-queue
Add ECDSA support for service account tokens
Fixes#28180
```release-note
ECDSA keys can now be used for signing and verifying service account tokens.
```
This implements the proposal in:
docs/proposals/secret-configmap-downwarapi-file-mode.md
Fixes: #28317.
The mounttest image is updated so it returns the permissions of the linked file
and not the symlink itself.
Before this change, Authorize() method was just returning an error,
regardless of whether the user is unauthorized or whether there
is some other unrelated error. Returning boolean with information
about user authorization and error (which should be unrelated to
the authorization) separately will make it easier to debug.
Fixes#27974
