Regenerate client secret” button for OAuth2/OpenID providers

### Is your feature request related to a problem?

When rotating an OIDC client secret today, the Client Secret field appears to support reveal/hide, but there is no obvious regenerate action. The admin has to manually generate a new secret outside Authentik, paste it into the provider, save it, then update the relying application. This works, but it is easy to miss and feels less safe than a built-in rotation workflow.

### Describe the solution you'd like

Add a button next to the Client Secret field, similar to:

- “Regenerate”
- confirmation dialog: “This will immediately invalidate the current client secret. Applications using this provider will fail authentication until updated.”
- generate a strong random secret server-side
- show/copy the new secret after regeneration
- save/update the provider

Why it helps:
This improves security hygiene, makes client-secret rotation discoverable, and reduces the chance of weak or incorrectly generated secrets.

### Describe alternatives that you've considered

The only other method I'm aware of is going to a shell and using openssl to manually create a new secret and paste it in.

### Additional context

_No response_