Update CircleCI config to sign MacOS binaries

[marinalimeira]

Description

We are already able to sign the binaries of internal projects, like patcher-cli and terrapatch-cli.

I am replicating the same process in git-xargs, the MacOS binaries will be signed and notarized before generating the sha256sum.

Related:

• Update CircleCI config to sign MacOS binaries terragrunt#2661
• Update CircleCI config to sign MacOS binaries cloud-nuke#559
• Update CircleCI config to sign MacOS binaries kubergrunt#209

Test release: https://github.com/gruntwork-io/git-xargs/releases/tag/v0.1.10-test-signing-binaries

TODOs

Read the Gruntwork contribution guidelines.

• Update the docs.
• Run the relevant tests successfully, including pre-commit checks.
• Ensure any 3rd party code adheres with our license policy or delete this line if its not applicable.
• Include release notes. If this PR is backward incompatible, include a migration guide.

Release Notes (draft)

Signing MacOS binaries from now on! 🎉

[marinalimeira]

Thanks for reviewing!