SSL related FN_NODE_CERT (and related) settings are
not very clear today. Removing this in favor of a
simple map of tls.Config objects. Three keys are
provided for this map:
TLSGRPCServer
TLSAdminServer
TLSWebServer
which correspond to server TLS settings for the
associated services.
Operators/implementers can further add more
keys to the map and add their own TLS config.
