Update JWT Policy documentation

[tech-Nico]

The JWT Policy documentation needs to be updated. Specifically, the documentation mentions that:

The policy prompts you to choose between three (GIVEN_KEY, GIVEN_ISSUER, GATEWAY_ISSUER) methods to retrieve the required public key.

This is actually not correct. The policy (as of 3.17.1) actually supports the following methods to retrieve the public key:

• GIVEN_KEY: You must provide a signature key as a resolver parameter according to the signature algorithm
• GATEWAY_KEYS: Look for signature key from API Gateway configuration according to issuer and kid from incoming JWT
• JWKS_URL: Retrieve JWKS from URL (Basically, URL ending with '/.well-known/jwks.json')