Implement version resolution

[mara-schulke]

Current State

As of right now buffrs users can only pin their dependencies which yields to a limited flexibility when using, especially in a fast moving environment.

Implementation Plan

In order to ship a proper version resolution for buffrs we need to rethink a couple of fundamental concept such as how we think about versioning, repositories and registries (see #235).

Once this is accomplished (and potentially already shipped) we can feed the version information from artifactory into pubgrub or resolvo to resolve a set of dependencies fulfilling all constraints.

Each pubgrub run should produce a new lockfile that is then written to disk (when doing a full resolution only from the lockfile, there should be no change!).

Also offline compatibility is key: If the cache contains all packages that are listed in the lockfile and the lockfile contains enough information to resolve the whole tree no network request should be made this is important for our nix integration and existing user workflows.

Things to watch out for

• It will not be possible to resolve multiple versions of the same package (this is due to limitations of how protoc works when compiling)
• It is desirable to use the existing caching implementation and lockfile implementation before doing any network requests. See the code in this PR for reference.
• It is desirable to only partially replace the lockfile if dependencies have been added.
• We should think about adding the project itself (read: the buffrs project containing the Proto.toml) into the lockfile to unify the top-level dependency graph with sub dependency graphs.