extract builder logic into new builder binary crate

[syphar]

Also

• moved CompressionAlgorithm to docs_rs_types crate.
• moved db::add_package into docs_rs_database crate.
• moved related things into builder crate (blacklist)
• moved doc_coverage types & parsing into _types crate
• I decided to start with new Config & Context structs, with some conversion
  in between, not migrating all the old code.
• to ease the migration I temporarily disabled the support for other registries in manual builds from the CLI
• there are some tests in the builder that also did web requests. I think
  I want to move these into "integration tests" which stay at the root of our
  project, when the migration of the other parts is finished. But IMO that's easier to do when the test-environment etc is more fleshed out.
• there are some things the main crate accesses from the builder-binary-crate,
  I probably need to move them to shared crates when I start migrating the other
  binaries later.
• the build_queue and queue_builder in the builder are just a MVP, a better structure is possible, but I want to do this separately.
• I'm not sure if I will have each binary have it's own TestEnvironment,
  or if I want to merge these.
• crate priorities move into the queue subcrate
• for now I didn't remove anything from the old cratesfyi binary. Like this
  I can start playing around with the new builder on the server without breaking
  anything.
• I'm not 100% certain about which CLI commands to move where yet. Current idea:
  we will have a docs_rs_cli (or _admin) binary for everything that just
  edits stuff in the database and the other services (web, watcher, builder)
  just pick it up. Inside the watcher/builder binary itself we would do things
  that need the full environment (index, build env, docker, ...).
• all the builder functionality is moved into the builder binary crate. The
  old binary uses the new build-binary as library and calls its functions.
• the file / module structure in the builder-binary is not final yet, but for now I want something merged before optimizing that later.