refactor: abstract apm client to a separate package

[kruskall]

Start working on decoupling apm and extension package.
Shutdown the apm receiver gracefully and move away from
deprecated ioutil calls.

Still untested but ready for review

[ghost]

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• Start Time: 2022-07-28T11:58:55.976+0000

• Duration: 8 min 0 sec

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Test	Results
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Total	260

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[axw]

Thanks, loving this refactoring.

Just one minor thing: "apm" feels too generic of a package name. Perhaps call it "apmproxy", or something along those lines?

[kruskall]

/test