OIDC provider should use NiFi keystore & truststore

The OIDC provider uses generic HTTPS requests to the OIDC IdP, but does not configure these requests to use the NiFi keystore or truststore. Rather, it uses the default JVM keystore and truststore, which leads to difficulty debugging PKIX and other TLS negotiation errors. It should be switched to use the NiFi keystore and truststore as other NiFi framework services do.