Merge pull request #1595 from porter-dev/belanger/add-docker-cache-option

Add `BUILDKIT_INLINE_CACHE` build arg to Docker builder

cli/cmd/docker/builder.go

@@ -62,6 +62,10 @@ func (a *Agent) BuildLocal(opts *BuildOpts) error {
 		buildArgs[key] = &valCopy
 	}
 
+	// attach BUILDKIT_INLINE_CACHE=1 by default, to take advantage of caching
+	inlineCacheVal := "1"
+	buildArgs["BUILDKIT_INLINE_CACHE"] = &inlineCacheVal
+
 	out, err := a.client.ImageBuild(context.Background(), tar, types.ImageBuildOptions{
 		Dockerfile: dockerfilePath,
 		BuildArgs:  buildArgs,