Don't resubscribe a project member when they leave a channel

[marcoieni]

Right now, team automatically adds project members to certain Zulip channels such as all/private. When a project members unsubscribes from these channels, team resubscribes them.
This shouldn't happen.

When team noticed a difference between subscribers to a channel and Rust Project members, team should distinguish these two cases:

• a new project member joins the Rust project, and so they need to be added to these channels.
• an existing member of the project unsubscribed from one of these channels.

Kobzol's proposal:

the solution for that is make the subscription edge-triggered, rather than level-triggered; subscribe once the person joins the team, unsubscribe once they leave. and if they unsubscribe themselves, just give them the possibility to resubcribe, but don't force it

[steffahn]

Another case (or set of cases?) is if the team repo changes. E.g. a new private channel is configured, or the definition of who should be (allowed) member changes.