add apt-cacher and vagrant-proxyconf

https://github.com/tmatilai/vagrant-proxyconf
https://github.com/tmatilai/apt-cacher-box

Start by reading the two linked projects, vagrant-proxyconf and apt-cacher-box, and inspect the repository's Vagrant entry points. The issue does not name files, tests, or expected behavior, so confirm how each should be integrated and what successful localserver provisioning should include before making changes.

Written by the indexing model from the issue text.