List Gateways and current Gateway in `gwa login`

[rustyjux]

Mimic the informative output from oc upon login:

Logged into "https://api.gold.devops.gov.bc.ca:6443" as "russell.vinegar@gov.bc.ca" using the token provided.

You have access to the following projects and can switch between them with 'oc project <projectname>':

  * b8840c-dev
    b8840c-prod
    b8840c-test
    b8840c-tools
    ec38a0-prod
    fe3a7e-prod

Using project "b8840c-dev".

WIP:

Waiting for authentication handshake...
✓ Successfully logged in using device login.

You have access to the following Gateways and can switch between them with 'gwa config set gateway <gateway-id>':

Display Name        Gateway ID  
Gateway gw-fdfee    gw-fdfee    
new-test111         gw-c168f    
RVINEGAR's Gateway  gw-ff064    
Tester              gw-44d2a    
This-namespace      gw-b963a    

Currently using: 
This-namespace  gw-b963a

Benefits:

• Existing users:
  • This saves users the need to run gateway list and/or gateway current to see what gateway is set.
  • Prompts user to change current gateway if invalid gw is set
  • (if we show host) may reduce confusion for users who use our test and prod envs
• New users:
  • Prompts user to create a new gateway and provides command directly within CLI

WIP in feature/ns-to-gw-login branch

To determine:

• include the host in login success message (api.gov.bc.ca, api-gov-bc-ca.test.api.gov.bc.ca, etc)
• should client cred login also list Gateways or show current Gateway? (or only list this info for device login?)
  • can service accounts even be attached to more than one Gateway?

To do for WIP:

• resolve errors on client cred flags (--client-id, --client-secret)
  • either don't run list and current for client cred, or stop passing those flags
• handle errors if an inaccessible or non-existing current gateway is set with a custom message
  • message: The current Gateway (gw-name) could not be accessed. Switch to a valid Gateway with 'gwa config set gateway'
• new user use case: set responses for when there are no existing gateways and/or no current gateway set

[timng-bcgov]

Thumbs up on the benefits for new and existing users. I think it's very helpful to have the host and user information in the success message.