Add sideload command

This adds pmbootstrap sideload:

usage: pmbootstrap sideload [-h] [--host HOST] [--user USER] [--install-key] packages [packages ...]

positional arguments:
  packages

optional arguments:
  -h, --help     show this help message and exit
  --host HOST    ip of the device over wifi (defaults to 172.16.42.1)
  --user USER    use a different username than the one set in init
  --install-key  install the apk key from this machine if needed

This runs the supplied package names through the pmbootstrap buildsystem to make sure they're up-to-date, then uses scp from the host to copy the built apks to /tmp on the phone and then installs them through ssh.

If the --install-key option is set then it will also copy over the apk key that's used for signing the packages built by pmbootstrap in case the postmarketOS install on the device isn't build by the same machine as you're sideloading from.

Closes #1649 (closed)