[BUG] REST API endpoint /users does not conform to best practices

Description:

Currently all actions on "users" with the REST API use unique endpoints.... ex. users.create, users.delete, users.get_avatar, etc.... where the userID is contained in the body. This does not conform to best practices because a GET on the endpoint /users itself should return a collection of users, and the path to perform actions on a specific user should include the "_id"....... ex. /users/{_id} with a GET, DELETE, PUT etc...

A good example of best practice is in the /livechat/departments endpoint, and it would be best if all REST API endpoints used the same design.

We are using terraform to configure users, omnichannel departments, omnichannel agents, etc.... and the users endpoint as is, is not compatible with terraforms 'destroy resource' strategy, and therefore it breaks our automation.

Start by locating the REST API definitions for /users and the /livechat/departments example mentioned in the issue. Compare their collection and item-route behavior, then trace the Terraform destroy workflow that currently fails. Done means users supports collection access plus /users/{_id} actions consistently with the stated REST design.