Gam users

[sseyda]

Docs: https://developers.google.com/ad-manager/api/reference/v202011/UserService.User

get_users_from_admanager function pulls information about GAM users. It can be used for further campaign filtering, especially when there are custom roles within network.

Few notes:

• query can be handled both with and without WHERE clause
• results of the query are appending to df line after line, and therefore all lines in final df have index 0
• according to doc, id, name, etc are not exactly dimensions, but I kept this name for consistency across functions

[dorotamierzwa]

Tested on Python versions 3.5 to 3.8