OIDC plugin: FAQ for JWS error message

## Definition of done
- add an FAQ like "Q: I'm getting a `only jwts are supported for the jws` error for the OIDC plugin, how do I fix it?" "A: The error "only jwts are supported for the jws" indicates that the OIDC plugin expects a JWT but received a JWS that is not in JWT format. To resolve this, ensure the token is in the correct JWT format, verify the plugin configuration, and ensure proper key management. If the issue persists, you may need to consult the documentation for your specific OIDC plugin and provider for more detailed guidance." on this page https://developer.konghq.com/plugins/openid-connect/#faqs

## Information
Slack: https://kongstrong.slack.com/archives/C046SPHV6AH/p1758835651102859
originally from Kapa

## Size
small

Open the OpenID Connect plugin documentation page and read its existing FAQs. Add the requested FAQ about the “only jwts are supported for the jws” error, keeping the answer accurate and consistent with the surrounding entries. Done means the FAQ appears under the page’s FAQs section with the proposed guidance.

Written by the indexing model from the issue text.