Require secrets to have types

[pleshakov]

Proposed changes

This PR introduces secret types that the Ingress Controller can support:

• kubernetes.io/tls for TLS secrets. Such secrets must have the tls.crt and tls.key keys.
• nginx.org/ca - for CA secrets. Such secrets must have the ca.crt key with a CA.
• nginx.org/jwk - for JWK secrets. Such secrets must include the jwk key with a JWK.

The Ingress Controller will no longer support secrets without the type field set to the types above.

[mikestephen]

Looking good!