feat: move logger to a separate package

[kruskall]

This is the last step to eliminate global state. Moreover,
'apmproxy' and 'extension' are now completely separate and
do not depend on each other.

[ghost]

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• Start Time: 2022-08-08T09:54:55.518+0000

• Duration: 7 min 17 sec

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Total	148

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[axw]

🎉

LGTM, but maybe we can cut down some of the repetition by using zaptest for constructing a logger. In the tests we can just panic/fail the test if the logger construction fails for some unexpected reason.