Allow extending teams from other teams

[rylev]

This PR allows extending team membership by the membership of another team. Concretely this PR changes the following:

• Team::members, Data::active_members, and Permissions::allowed_people now all return a Result since getting all members can fail if an included team does not exist.
• Added Team::contains_person to test whether a team contains a person as a member
• Made wg-leads a marker team instead of a working group
• Created a project-group-leads marker team
• Removed the use of the various special "include-*" options from all teams except for the special marker teams that those options exist for. All other teams that also want to include those members, can use included-teams instead.

And lastly, the entire point of this PR:

• Made the inside-rust-reviewers include the leadership council

[Mark-Simulacrum]

Hm, this seems good (looks like CI is failing). For the specific use case of council it probably makes sense to just grant write permissions in general on the repo rather than just inside rust.

But happy to approve once CI is fixed.

[rylev]

@Mark-Simulacrum done