builder: add worker gc policies and labels

[crazy-max]

needs #1430

Adds builder GC Policies with worker labels. Will be displayed when using inspect command:

$ docker buildx inspect
Name:          builder2
Driver:        docker-container
Last Activity: 2022-11-30 12:42:47 +0100 CET

Nodes:
Name:           builder20
Endpoint:       unix:///var/run/docker.sock
Driver Options: env.BUILDKIT_STEP_LOG_MAX_SPEED="10485760" env.JAEGER_TRACE="localhost:6831" image="moby/buildkit:latest" network="host" env.BUILDKIT_STEP_LOG_MAX_SIZE="10485760"
Status:         running
Flags:          --debug --allow-insecure-entitlement security.insecure --allow-insecure-entitlement network.host
BuildKit:       v0.10.6
Platforms:      linux/amd64, linux/amd64/v2, linux/amd64/v3, linux/arm64, linux/riscv64, linux/ppc64le, linux/s390x, linux/386, linux/mips64le, linux/mips64, linux/arm/v7, linux/arm/v6
Labels:
 org.mobyproject.buildkit.worker.executor:         oci
 org.mobyproject.buildkit.worker.hostname:         docker-desktop
 org.mobyproject.buildkit.worker.network:          host
 org.mobyproject.buildkit.worker.oci.process-mode: sandbox
 org.mobyproject.buildkit.worker.selinux.enabled:  false
 org.mobyproject.buildkit.worker.snapshotter:      overlayfs
GC Policy rule#0:
 All:           false
 Filters:       type==source.local,type==exec.cachemount,type==source.git.checkout
 Keep Duration: 48h0m0s
 Keep Bytes:    488.3MiB
GC Policy rule#1:
 All:           false
 Keep Duration: 1440h0m0s
 Keep Bytes:    24.21GiB
GC Policy rule#2:
 All:        false
 Keep Bytes: 24.21GiB
GC Policy rule#3:
 All:        true
 Keep Bytes: 24.21GiB

[crazy-max]

Atm it returns GC Policies and labels only for the default worker.

[jedevc]

Hm, this does make the output a bit noisier, and the policies are slightly tricky to mentally parse. I wonder if the GC policies should be hidden behind a verbose flag? Not sure about this, it's definitely useful information, but probably not to the average user.

I think the labels should be good without that, they're not too long.

[crazy-max]

Hm, this does make the output a bit noisier, and the policies are slightly tricky to mentally parse.

Yeah that's noisy but still relevant and for parsing we should do smth like #830 (comment)

I will move Platforms before Labels.

[jedevc]

LGTM, but we should make sure to get the follow-up to tidy the output and parsing into the same release as this.

[crazy-max]

Yes and also another follow-up for our actions toolkit: https://github.com/docker/actions-toolkit/blob/8cb1698b203083ee1c3996cbd2a0d197cae79d9f/src/buildx/builder.ts#L57

[jedevc]

@crazy-max @tonistiigi, anything blocking this?