Add ability to define a file based scheme for jwks_uri in EndUserAuthenticationPolicySpec

[my3sons]

We have a JWT scenario where the public key that is used to verify the signature of the JWT is mounted to the pods via a Kubernetes secrets volume. Therefore, we need the ability to define a file location scheme value for the jwks_uri property that is associated to our EndUserAuthenticationPolicySpec. Currently, only the http and https schemes are supported.