feat(ubuntu): Install brew package manager on x86_64

[cdalvaro]

Add Homebrew package manager to Ubuntu (x86_64) machines.

This package is needed to allow brew testability on Linux machines after having extended the mac_brew_pkg.py module to allow Linux in saltstack/salt#66609

[cdalvaro]

I'm sorry, @twangboy. I didn't escape a $ sign properly. I think now is right.

[cdalvaro]

It seems installation has failed:

[14:11:49] ==> amazon-ebs.image: Provisioning with shell script: /tmp/packer-shell1663122472
           ==> amazon-ebs.image: + [[ x86_64 == x86_64 ]]
           ==> amazon-ebs.image: /tmp/script_4580.sh: 2: [[: not found

I'll try a different approach.

[cdalvaro]

I'm not sure if there's a more appropriate user than ssh_username for installing brew.

[twangboy]

@cdalvaro I wanted to give you a heads up on this. We're being asked to make a major migration of our CICD off of AWS by the end of the month. This is probably going to affect our testing for awhile till we get it all worked out. So, we're going to hold off on this until things settle down.