chore: dynamic help_text for client_secret

[lrq315]

Fixes #1628

Description of the Change

• dynamic help text for client_secret based on hash_client_secret in both the Admin and Registration forms
• add Chinese translation; remaining updates will be handled in a separate PR
• fix the local test-idp for e2e testing
  
  

Checklist

• PR only contains one change (considered splitting up PR)
• unit-test added
• documentation updated
• CHANGELOG.md updated (only for user relevant changes)
• author name in AUTHORS
• tests/app/idp updated to demonstrate new features
• tests/app/rp updated to demonstrate new features

[n2ygk]

Wow, that's a lot of changes. @dopry are you OK with this much code change to implement this relatively minor UI fix?

Also please wait on #1631 to be merged and rebase to resolve the failed 3.14 test.

[lrq315]

Sorry—looking back, it does seem that the changes may have been a bit over-scoped. I should have checked with you on the scope in advance. Please feel free to let me revert the form changes and just update the text directly.

As for the other E2E test IdP mitigations, I think they might still be helpful for others.