protobuf: remove gogoproto

Removes gogo/protobuf from buildx and updates to a version of
moby/buildkit where gogo is removed.

This also changes how the proto files are generated. This is because
newer versions of protobuf are more strict about name conflicts. If two
files have the same name (even if they are relative paths) and are used
in different protoc commands, they'll conflict in the registry.

Since protobuf file generation doesn't work very well with
`paths=source_relative`, this removes the `go:generate` expression and
just relies on the dockerfile to perform the generation.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

vendor/github.com/moby/buildkit/cmd/buildkitd/config/config.go

@@ -154,10 +154,29 @@ type ContainerdRuntime struct {
 }
 
 type GCPolicy struct {
-	All          bool      `toml:"all"`
-	KeepBytes    DiskSpace `toml:"keepBytes"`
-	KeepDuration Duration  `toml:"keepDuration"`
-	Filters      []string  `toml:"filters"`
+	All     bool     `toml:"all"`
+	Filters []string `toml:"filters"`
+
+	KeepDuration Duration `toml:"keepDuration"`
+
+	// KeepBytes is the maximum amount of storage this policy is ever allowed
+	// to consume. Any storage above this mark can be cleared during a gc
+	// sweep.
+	//
+	// Deprecated: use MaxStorage instead
+	KeepBytes DiskSpace `toml:"keepBytes"`
+
+	// MinStorage is the minimum amount of storage this policy is always
+	// allowed to consume. Any amount of storage below this mark will not be
+	// cleared by this policy.
+	MinStorage DiskSpace `toml:"minStorage"`
+	// MaxStorage is the maximum amount of storage this policy is ever allowed
+	// to consume. Any storage above this mark can be cleared during a gc
+	// sweep.
+	MaxStorage DiskSpace `toml:"maxStorage"`
+	// Free is the amount of storage the gc will attempt to leave free on the
+	// disk. However, it will never attempt to bring it below MinStorage.
+	Free DiskSpace `toml:"free"`
 }
 
 type DNSConfig struct {