feat(rust): implement a new software service in Rust

[imobachgs]

Warning

This code is still a work in progress and so functionality is missing or temporary. The PR is open against the product-registration branch.

This PR implements a new version of the software service using our libzypp bindings. The API is exposed through the /api/software_ng namespace, so it can coexist with the old software service.

Architecture

This solution makes heavy use of channels. The software service is composed of two parts:

• SoftwareServiceServer which implements the service logic. It runs as an independent Tokio task and receives the requests using a channel.
• SoftwareServiceClient which is just a wrapper around the channel to send messages.

This approach is quite flexible, as the server is always running (so it could listen to other events) and processes one action at a time (it is hard to get into a deadlock), and it is fairly easy to reason about. The downside is that it requires some boilerplate code.

Note

I would like to experiment with a simpler approach based on mutexes, but it can wait a bit.

Tasks

• Put the foundations of the new software service.
• Improve ProductsRegistry to handle the filters by architecture.
• Add an alias or name to the list of repositories.
• Import the GPG keys (waiting for the C-API).
• Select the product if there is a single one.
• Emit an event when the product is selected.
• Implement product selection.
• Implement /probe.
• Run the probe on a separate Task so it does not block (see the manager's example although it is not part of our codebase yet, but you get the idea).
• Implement /proposal.
• Implement /resolvables/:id.
• Implement the list of patterns (/patterns)
• Implement patterns selection (as part of PUT /config).
• Implement /install.
• Add issues support (under /issues).
• Implement the registration logic.