feat(apmgrpc): wrap the server-stream with transaction-ctx

[bendiktv2]

This allows the handler to retrieve the transaction from it's context, to e.g. create spans.

This closes #1148

[apmmachine]

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• Start Time: 2021-11-15T12:04:44.067+0000

• Duration: 33 min 46 sec

• Commit: 53ec384

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[stuartnelson3]

Looks good to me, but I'll wait for @axw for final approval. He'll be back next week.

[axw]

Thanks for the PR! The approach looks good, I'd just like to avoid the dependency please.

[axw]

Thank you :)

[axw]

/test

[axw]

/test