Support for Vagrant's built-in chef installer

[patcon]

An installer is currently built right into the default chef provisioners, so it seems vagrant-omnibus is now only required for advanced usage (if at all).

https://docs.vagrantup.com/v2/provisioning/chef_common.html

Would be great to set the default chef.installer_download_path to the one we already use for vagrant-omnibus. For now, I'm just manually setting it to use chef's file_cache_path, which already has a bucket when chef provisioners are used.

[fgrehm]

Hey, sorry for the silence here but this project is looking for maintainers 😅

As per #193, I've added the ignored label and will close this issue. Thanks for the interest in the project and LMK if you want to step up and take ownership of this project on that other issue 👋