Add a new build argument for Packer version

Users can now specify the packer release version via the new packerVersion argument.

Bump Packer to v1.6.4

It would be nice if we can override this via the argument. However, I haven't figured out how to do this yet

Simplify Packer Arguments

Assuming users know how to user Packer, the additional Error Handlings I added seem to be unnecessary.

Version 0.1 Release

Very basic GitHub Action that supports HCL Packer AMI Build