Allow team_id argument for users.list method

[ronanmurphy168]

Is your feature request related to a problem? Please describe.

According to the Slack API docs, the users.list method requires the team_id argument when using an org-level token. The Slack App we are using is an org-level app so we are unable to use the current listUsers method in this client.

Describe the solution you'd like

We would like to request a new listUsers method which accepts the team_id as an argument.

Describe alternatives you've considered

We tried to make our app use a regular token instead of an org-level token. We discovered that once a Slack app has been set as org-level, this cannot be undone.