JWS_URI caching removed when keyCache is omitted

[jasonwilliams14]

The keyCache value in jwks policy is a required value. This requirement is not being enforced.
When keyCache is omitted, it removes all the caching pieces for jwks_uri.

This is what the .conf looks like when keyCache is omitted (removing all caching)

    auth_jwt "MyProductAPI" token=$http_token;

    auth_jwt_key_request /_jwks_uri_server;

    location = /_jwks_uri_server {
        internal;
        proxy_method GET;
        proxy_set_header Content-Length "";


        proxy_set_header Host login.microsoftonline.com;
        set $idp_backend login.microsoftonline.com;
        proxy_pass https://$idp_backend/<removed>/discovery/v2.0/keys;

    }

Here is the policy used for the above .conf output

apiVersion: k8s.nginx.org/v1
kind: Policy
metadata:
  name: jwt-policy
spec:
  jwt:
    realm: MyProductAPI
    token: $http_token
    jwksURI: https://login.microsoftonline.com/<removed>/discovery/v2.0/keys

Here is the expected .conf output we want to ensure caching of the JWT public keys:

    auth_jwt "MyProductAPI" token=$http_token;


    auth_jwt_key_cache 1h;
    auth_jwt_key_request /_jwks_uri_server;

    location = /_jwks_uri_server {
        internal;
        proxy_method GET;
        proxy_set_header Content-Length "";

        proxy_cache jwks_uri;
        proxy_cache_valid 200 12h;


        proxy_set_header Host login.microsoftonline.com;
        set $idp_backend login.microsoftonline.com;
        proxy_pass https://$idp_backend/<removed>/discovery/v2.0/keys;

    }

Here is the policy that has beeb configured for the above .conf output:

apiVersion: k8s.nginx.org/v1
kind: Policy
metadata:
  name: jwt-policy
spec:
  jwt:
    realm: MyProductAPI
    token: $http_token
    jwksURI: https://login.microsoftonline.com/<removed>/discovery/v2.0/keys
    keyCache: 1h

### Tasks
- [x] Design tests to capture invalid and valid inputs
- [x] Implement correct validation logic based on the rules in NIC docs
- [x] verify if python tests need to be updated

### Tasks