this complexity is no longer necessary now that you can just forward a
runtime service over gRPC

Revert "refactor buildkit addr defaults into runtime pkg"

This reverts commit 5d27026.

Revert "resolve defaults in main rather than runtime init"

This reverts commit 50e0fad.

Revert "simplify RuntimeAddrs"

This reverts commit 151e72d.

Revert "add SetService helper"

This reverts commit 7c63a99.

Revert "give addrs a distinct section in runtime config"

This reverts commit c888a43.

Revert "use buildkit runtime defaults in tests"

This reverts commit 8b7a0d1.

this should make getting started _much_ easier - you don't need to
manually set up a Buildkitd daemon, it just runs the matching version in
Docker.

original license (Apache) and notice preserved.

this should be made configurable and op-in someday

no more manual buildkit setup!