refs #4515 - cache apipie docs on installation

Tested on nightly and tested the command on 1.4 successfully.

This caches the API docs (like https://github.com/theforeman/foreman/commit/0527e75be3647c1e89b8fd19d2e3cee00d07aa38#diff-f253775911a09d6068d2a99e41a60bd8R537) after installation so Hammer can fetch the JSON docs from the Foreman server for dynamic bindings.