Implement service account CRUD commands

[craicoverflow]

This PR implements the service account CRUD API into the CLI.

Verification

1. Create a service account:

$ rhoas serviceaccount create -o json --name my-svc-acct

2. Reset credentials for a service account

$ rhoas serviceaccount reset-credentials --id <svc-acct-id> -o json

3. Delete a service account

$ rhoas serviceaccount delete --id <svc-acct-id>

4. List all service accounts in your user organisation

$ rhoas serviceaccount list