feat: add `build-into` subcommand

[wolfv]

This is the start for adding a build-into subcommand to rattler-build. The idea is that we build the package "into" a channel, which means we will also upload and index the channel after a successful build, giving users of S3 buckets or local filesystem channels a "one-stop" solution to their Conda packaging needs.

For a channel on prefix.dev or Anaconda, we would just upload (and not run a manual indexing, of course).