o git_repo / cargo2: support dulwich 1.x (and drop support for < 0.24)
o git_repo: don't read global config files (consistent behaviour with LFS)
o cargo: new element plugin for building with cargo (not to be confused with
  cargo source plugin)
o gnu: expose in project.conf / entrypoints so that it can be used
o cargo2: report per-crate provenance info (requires upcoming buildstream 2.7)
o cargo2: fix handling of workspace dependencies