Create `bbctl update bbctl` command for binary installations

Create a bbctl update bbctl command. This root command will be used in the future for updating the individual application charts but we should treat the bbctl target as a unique case for upgrading the client itself.

Acceptance Criteria

• When run, bbctl should print out instructions to the user to update to the latest version of bbctl using curl / tar commands to download a new binary.
• The suggested URL should note the correct, latest release
• Support an optional --version parameter to generate a download link for a previous version