Add Chef Automate support to inspec compliance login

[chris-rock]

The goal is to support Automate logins via inspec compliance login without requiring the existing login_automate.

Right now we have to different login methods for Chef Compliance and Chef Automate. We should harmonize those:

• inspec compliance login_automate https://automate.compliance.test --insecure --user='admin' --ent='brewinc' --usertoken='%TOKEN%
• 'inspec compliance login https://compliance.test --insecure --user='admin' --token='%TOKEN%'`

As you can see from the examples, only token and ent argument are different. We should use --token as the default and make --ent an optional argument. We may need a --type to indicate if this is a Chef Compliance or Automate server.

This issue should:

• add Automate support to the login command (using the --token and --ent flag as required)
• continue to support the --usertoken flag but output a deprecation warning
• add a deprecation warning to the login_automate command

The removal of the login_automate command will come via a later change via #2154 in the next appropriate major release.