[BEAM-7507] Use TextFormat to escape workIds to a string rather than utf8

[steveniemitz]

In StreamingDataflowWorker, when setting the workId for the logging MDC, currently the code attempts to decode a binary blob as utf8. This will (generally) cause a decoding error, and the java UTF8 decoder uses a globally synchronized cache to handle generating these error results. This can result in lock contention at high input rates.

This simply changes it to use protobuf's TextFormat to escape the bytes to a string, preserving human readability for keys with text in them.

@lukecwik

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