mirror subscription: Catch up with SDK changes

[gregscullard]

Detailed Description
Mirror node is going to start rejecting calls to subscribeTopic for topics that don't exist and return GRPC NOT_FOUND.
Will also reject calls with an entity that does exist but is not a topic with INVALID_ARGUMENT.
The SDK will:
When "NOT FOUND", try again with exponential back-off, eventually give up with error.
When "INVALID_ARGUMENT" give up with error

Actual Behavior
mirror subscription and relay don't handle these error situations

Expected Behavior
Handle error from SDK