Allow overriding OS_TYPE and ARCH. This will allow signing locally on e.g. mac

[onetechnical]

Summary

To execute make sign you need to be able to issue the signing command. There is a script for this, but it presumes that the architecture you're signing for is the same as what you're running.

This is problematic if you are on mac, as OS_TYPE will register as darwin. To override this, we allow you to override OS_TYPE, e.g. set it to linux. We will also allow overriding ARCH, since this may be set to arm64 on newer macs.

Test Plan

Verify signing works with these new changes, e.g.:

ARCH=amd64 OS_TYPE=linux make sign

[egieseke]

Makes sense.

[codecov-commenter]

Codecov Report

Merging #595 (f32ecc7) into develop (c454446) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop     #595   +/-   ##
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  Coverage    47.55%   47.55%           
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  Files           25       25           
  Lines         3863     3863           
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  Hits          1837     1837           
  Misses        1745     1745           
  Partials       281      281           

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[algobarb]

Since this is for signing, would this change only affect our team? Also, would we get a help message or some doc so we know we can pass in these new variables as described in the test plan ARCH=amd64 OS_TYPE=linux make sign ?

[onetechnical]

Since this is for signing, would this change only affect our team? Also, would we get a help message or some doc so we know we can pass in these new variables as described in the test plan ARCH=amd64 OS_TYPE=linux make sign ?

Correct, this is internal only. I am updating the release doc right now.