Merge upstream moby/buildkit changes

[janishorsts]

The current EarthBuild/buildkit is behind the upstream moby/buildkit.

The merge strategy needs to be established to simplify the upgrade process and document the EarthBuild changes in fork-specific MD files, thereby easing future maintenance.

The last merge was probably:

$ git log origin/main --merges -n 1
commit 531b303aa8ec03c29c2ceaa140eb0a6d32e6f6f3 (upstream/earthly-main)
Merge: 594835b59 e163acdbb
Author: Brandon Schurman <brandon@earthly.dev>
Date:   Wed May 15 16:05:21 2024 -0400

    Merge pull request #59 from earthly/brandon/http-proxy
    
    Allows option for client to use grpc default dialer. The builtin dialer in gRPC has support for things like HTTP connect proxy which we need to support BYOC satellites in some environments. Buildkit was previously forcing it's own dialer implementation.