fix: improve stability of build agent packer scripts, remove variables that aren't needed

[jorisdon]

Issue number: Closes #308

Summary

Changes

This PR does two things:

1. It improves the stability of build agent packer scripts, mainly by setting dpkg timeout parameters that ensure that dpkg locks (e.g. those acquired by SSM automation) don't impede installation of packages (on Ubuntu) and using dnf instead of yum (on Amazon Linux 2023).
2. It removes configuration variables that weren't used.
3. It lowers the WinRM connection timeout from 1 hour to 15 minutes, to give faster feedback in case firewalls are blocking WinRM connections.

User experience

Only change in user experience is that there should now be fewer packer build failures.

Checklist

If your change doesn't seem to apply, please leave them unchecked.

• I have performed a self-review of this change
• Changes have been tested
• Changes are documented

I checked, but documentation changes are not necessary for this PR.

Is this a breaking change?

No

Acknowledgment

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[kylesomers]

Include the WinRM timeout configuration from #309 in this PR then we can close out that one.

[henrykie]

Approving.

We should look to combine these AMI builds under a single template to reduce duplicate config. Packer is build to provision multiple AMIs off various sources in one template. Not a priority.