Implement RO-crate creator

[PeterKraus]

This PR implements RO-crate creation once the payload completes and creates a NetCDF file. See this MADICES discussion for further info about how the RO-crates are structured.

This PR depends on Payload-2.2, which now makes specifying a User.identifier mandatory. It will also by default include a directive for RO-crate upload to the default repository (which will do nothing unless configured below).

The RO-crate capability can be enabled by first installing tomato with the [rocrate] option (which installs the required deps), and then configuring at least the repositories.default.endpoint and repositories.default.api_key in the settings file. If the payload.settings.output.repositories contains a match with the entries in the settings file repositories section, a RO-crate will be created.

Multiple repositories can be configured in the tomato settings file. Neither the endpoint nor the api_key (or any other config option within the repositories section of the settings file) is included in the NetCDF (or the RO-crate) file, so API keys should not leak in this way.

Upload mechanism to follow, see https://github.com/MADICES/our-crate.

Tagging @ml-evs.