Support for plugins

[lburgazzoli]

Feature or problem description

• As a service owner I would like to provide a sub command for a service I'm contributing without having to bake my code in the rhoas cli but at the same time, leveraging all the authentication and common feature provided by rhoas
• As a service consumer I would like to enhance the rhoas client UX by providing to tailor it to my needs or to provide enhanced capability

Proposed solution

rhoas should provide a pluing mechanism similar to kubectl and krew so services/operations can provide their own subcommands.

As example we may think that a new service foo could be made available to the rhoas cli by installing a related plugin

rhoas plugin install foo

From that point on, the service can be consumed as any other service available in rhoas:

rhoas foo bar

Additional context

This would help also to release new version of service specific plugin without having to release the entire cli