Make cargo owners consistent and ensure it stays so

fontations, fontc, and sleipnir crates appear to have inconsistent owners. To fix:

- Setup a GH team and make it owner of all our crates
- https://doc.rust-lang.org/cargo/reference/publishing.html#cargo-owner
- Setup CI to check the team is assigned as owner for all crates
- I believe https://doc.rust-lang.org/cargo/commands/cargo-owner.html can be used to list for this purpose

Start by reviewing the Cargo owner and cargo owner documentation linked in the issue, then inventory the fontations, fontc, and sleipnir crates. Done means one GitHub team owns all crates and CI checks that ownership remains consistent.

Written by the indexing model from the issue text.