Include dpkg frontend lock in APT_LOCK_FILES (SC-650)

[TheRealFalcon]

Additional Context

#1034 (comment)
#1034 (comment)

I also included a link to the first comment in a code comment.

[blackboxsw]

Thanks for the James. Reasonable to add yet another apt lock file check without additional unittests as we already have coverage for this functionality.

I was able to continue to validate that desired behavior and retries is working by camping on an apt upgrade in a terminal and running cloud-init modules --mode=final with userdata which tries to install packages

2021-12-15 03:21:07,618 - debian.py[DEBUG]: Waiting for apt lock
2021-12-15 03:21:17,631 - debian.py[DEBUG]: apt lock available
2021-12-15 03:21:17,631 - subp.py[DEBUG]: Running command ['eatmydata', 'apt-get', '--option=Dpkg::Options::=--force-confold', '--option=Dpkg::options::=--force-unsafe-io', '--assume-yes', '--quiet', 'update'] with allowed return codes [0] (shell=False, capture=False)