We have internal service for employee images and in that service we have API for fetching user image.

We would like to be able to set user avatar as URL to that service so that avatar is not downloaded into Rocket.Chat configured storage.

Example:
For user test service URL would be https://acme.com/api/v1/test and service call returns PNG/JPEG image (depending on what type of image user uploads).

Rocket.Chat for user avatar provides /avatar/{username} which loads user avatar from configured storage.
Provide a way to either change /avatar/{username} to https://acme.com/api/v1/{username} or maybe easier approach would be performing HTTP.302 - Redirect to https://acme.com/api/v1/{username} from /avatar/{username} when accessed.