Allow OAuth 2.0 Device Authorization Grant to authenticate

[knikolla]

The script to register users currently requires a service account to authenticate with Keycloak, however Keycloak also supports OAuth 2.0 Device Authorization Grant. This is the flow in which the CLI generates a code and link, you open a browser and authenticate using that link, which gives you a token, and you insert that into the CLI. This is the flow that you authenticate to streaming services on your TV and the flow that OpenShift uses for CLI authentication.

If we support/document this flow, we can allow users to interact with the API through the CLI without requiring a Keycloak service account.

If we additionally support #11 we could allow PIs themselves to bulk add through the script.