[v0.13] allow driver-opt to that sets bridge network as default

[tonistiigi]

Description

BuildKit v0.13 comes with support for bridge networking. It is not default in v0.13 but is planned to become default in v0.14 . There should be a easy way to configure builder to use bridge already in v0.13 so we can do some extended testing.

[TBBle]

In my brief testing, it seems that apart from a couple of missing binaries in the BuildKit image, --buildkitd-flags "--oci-worker-net=bridge" was sufficient to make the Bridge mode work, so this would just be a UX feature, I guess? And given that we want bridge mode to be the default in 0.14, a rather temporary UX feature at that.

Edit: Hidden earlier comments, that I've realised were probably off-track.

Does this request include making custom network DNS work with bridge mode somehow, to avoid the need for docker buildx build --network host?

If not, I'm not sure I understand the value of a driver option over --buildkitd-flags "--oci-worker-net=bridge".