Planemo without public internet

Given current GH outage, would be prudent that we add a flag to skip outbound network requests. E.g. for non-required things like updating gx_repo, it would be skipped. For required things (?) we would error.

Search the Planemo CLI entry points for outbound network requests and existing option definitions. Trace which requests are optional versus required; done means a flag skips optional requests while required requests still report an error, with tests covering both paths.

Written by the indexing model from the issue text.