Resolve "Add "check for new version" functionality and enable it as part of startup"

General MR

Summary

This MR adds update checks on invocation to bbctl. It does not yet perform any updates as that functionality is being written in another ticket. I decided to make the update checking modular to accommodate situations where a release may have been cut upstream but it's not yet released with the installation method used to install bbctl. We don't want to prompt them to update when they can't, after all. As installation methods become available, logic can be added to determine exactly how bbctl was installed and version checking specific to that installation method can be invoked at runtime.

Relevant logs/screenshots

Up to date:

Out of date:

Very out of date:

Update checking skipped (--skip-update-check or SKIP_UPDATE_CHECK=true):

Linked Issue

Furthers #293 (moved)

Upgrade Notices

N/A