Use nicer error message for login nonce error

[nwmac]

Summary

Fixes #13256

Occurred changes and/or fixed issues

This PR adds handling of the nonce error and displays a non-offensive error in this case.

Testing is difficult, since its hard to generate this error case, however, this has been implemented such that the handling is done in the login page, so you can test by going to:

https://<RANCER_URL/auth/login?err=nonce

You should now see the friendly error message instead of the previous error message.

Screenshot/Video

After this PR:

Checklist

• The PR is linked to an issue and the linked issue has a Milestone, or no issue is needed
• The PR has a Milestone
• The PR template has been filled out
• The PR has been self reviewed
• The PR has a reviewer assigned
• The PR has automated tests or clear instructions for manual tests and the linked issue has appropriate QA labels, or tests are not needed
• The PR has reviewed with UX and tested in light and dark mode, or there are no UX changes

[richard-cox]

There's a 50/50 comment, but could merge without it.

Also gave it a test with github and manually breaking the nonce, functionality worked fine

[richard-cox]

wondered if we should also change this, as it's in the url. higher risk, it's not an un-factual state and would help product support though