Deploy tokens

[w4]

We should provide a way for crate owners to generate "deploy tokens" which are tokens that can be passed to cargo --token, that'll only have permission to publish to that crate

We also need a way to provide CI access to the private crates, maybe just personal access tokens? that'll take the place of the deploy token too since CI will just act as a normal user of chartered, just using a password (personal access token) for SSH auth.

This can be worked around for now by giving CI an SSH key and creating a normal account in chartered

[w4]

These days I'm thinking 'access tokens' like they're implemented in https://github.com/w4/gitlab-cargo-shim for CI could fit the bill