Add support for Okta oauth2 integration

[maheshlokhande1]

As per discussion we will now be adding okta commands like this:

For username password based authentication with Client credentials

lmctl login https://cp4na_endpoint --okta --client client_id> --client-secret client_secret> -u username -p password --scope lmctl --auth-address https://okta_endpoint --auth-server-id default

For only client credentials lmctl login --okta --client client_id --client-secret client_secret --auth-server-id default --auth-address https://okta_endpoint https://cp4na_endpoint --save-creds

We will introduce new flag ‘--okta’ which will indicate okta authentication to use in lmctl. Also ‘auth-address’ parameter will contain okta auth server api endpoint and ‘cp4na-endpoint’ will contain cp4na cluster endpoint. Parameter auth-server-id will contain Okta server's backend authentication server used. Parameter scope will be the scope defined for user's authentication in Okta server's backend authentication server.

Please find attached doc for Okta server settings used. Okta_settings.docx

[dvaccarosenna]

Fixed by #161