Write Pulsar message-receiving client for testing

[richscott]

Using the data defintions and logic in internal/pulsarutils/pulsarclient.go and messageid.go, write a basic Pulsar client program that (optionally, authenticates first) to a Pulsar cluster, and continuously polls (select's) from a channel as supplied by the Receive() func in internal/pulsar/async.go. Connection configuration should be specifiable via command-line flags.

Interrupting the program (ctrl+c / SIGINT) should close the context and terminate the program.

This issue is part of the suite of tools specified in #1460.

[dave-gantenbein]

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