tracking r/sys/teams work.

[irreverentsimplicity]

Description

This issue documents the work on r/sys/teams package in this PR: #2957.

Initial plan:

• using users.User type for members
• a team can have an arbitrary name inside the struct, on top of the address
• adding a Permissions []string, which allows for arbitrary, realm-defined permissions, cross-matched with a team member.

Trying to follow #2195

[moul]

Opening a companion issue for a PR after it has been created, especially when the PR is already targeting an existing issue, complicates tracking. Therefore, I will close this. If you want to keep track of your PR, please do so within the PR itself. For general questions about the original issue, please ask them there.