[OpenID4VCIFrontend] Interoperability issues - Relative URLs in Credential Issuer Metadata

**Description:**
In OpenID4VCIFrontend the metadata hosted at` /.well-known/openid-federation` incorrectly uses relative paths (e.g., `/credential`) instead of absolute HTTPS URLs for its service endpoints.

The affected parameters in the credential_issuer object include:

- pushed_authorization_request_endpoint
- authorization_endpoint
- token_endpoint
- credential_endpoint
- nonce_endpoint
- deferred_credential_endpoint
- revocation_endpoint
- status_assertion_endpoint
- notification_endpoint

**Reference:**
The OpenID4VCI standard requires these endpoints to be valid HTTPS URLs to ensure interoperability with standard-compliant Wallets.