Add release automation on tag push

[sondavidb]

Issue #, if available:
#447

Description of changes:
Created a new workflow for automating part of the release process. On tag push, it will test the build on AMD64, create the binaries + sha256 checksums, and create a draft release with a changelog. Note that testing and building are run in parallel, which was an intentional design choice, but if we feel that the tests should pass before building the binaries, that can be changed.

ARM64 releases must still be created manually. Technically we could build the binaries with ARM64 here anyway but it would be considered poor practice to test and build in separate environments. (Still waiting for GH Actions to natively support ARM64 :v)

Testing performed:
I pushed a tag and ensured the workflow passed. You can see it running successfully here. The workflow was modified to include a THIRD_PARTY_LICENSES file, but otherwise is identical to the one in this PR. The workflow was triggered with the following:

git tag -s -a v999.999.999 -m "Release v999.999.999"
git push origin v999.999.999

The created release can be seen here (release will be deleted after PR is merged). Note that the changelog is empty. My guess is that this is due to previous testing with other tags making GitHub erroneously believe the last release was the tag previously pushed and deleted. This should not be an issue for official releases, but if a release needs to be modified for whatever reason, please bear in mind it may generate an empty changelog, so we should ensure we keep the original generated changelog.

To be explicit, this is not an official v999.999.999 release :P

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[austinvazquez]

I noticed the test release did not have the release version in the artifacts. Has that been resolved?

[sondavidb]

I noticed the test release did not have the release version in the artifacts. Has that been resolved?

Thanks for the catch. Looks like you can't refer to GH environment variables within the same step that they're assigned. Fixed that up by just using a local variable.

[austinvazquez]

LGTM. Thanks.

[sondavidb]

Moved all binary compiling logic to a separate script and created a Makefile target for release, per previous discussions. This should allow for a slightly smoother process for automating releases on ARM64, which currently has to manually test and set up everything.

[sondavidb]

Poorly-handled merge conflicts, sorry about that x.x