add cache_to option and remove manual image pull (#46)

Port from https://github.com/thegeeklab/drone-docker-buildx/pull/124

Basically docker cache got a bit fancier and now includes a cache manifest. Manually pulling these containers isn't sufficient enough, so remove the manual pull.

cache_to allows you to push your cache including a manifest to a remote location: https://docs.docker.com/engine/reference/commandline/buildx_build/#cache-to

Unfortunately this option isn't quite that useful: to fully use this feature, you need to supply your arguments in CSV format, which woodpecker unhelpfully splits into multiple completely separate arguments, breaking it :(

With a further change to fix that issue I managed to turn a multistage rust build from ~3 minutes down to 20 seconds.

Co-authored-by: miniduikboot <mini@duikbo.at>
Reviewed-on: https://codeberg.org/woodpecker-plugins/plugin-docker-buildx/pulls/46
Reviewed-by: 6543 <6543@obermui.de>
Co-authored-by: miniduikboot <miniduikboot@noreply.codeberg.org>
Co-committed-by: miniduikboot <miniduikboot@noreply.codeberg.org>

plugin/docker.go

@@ -10,15 +10,6 @@ import (
 	"github.com/urfave/cli/v2"
 )
 
-// helper to check if args match "docker pull <image>"
-func isCommandPull(args []string) bool {
-	return len(args) > 2 && args[1] == "pull"
-}
-
-func commandPull(repo string) *exec.Cmd {
-	return exec.Command(dockerExe, "pull", repo)
-}
-
 func commandLoginEmail(login Login) *exec.Cmd {
 	return exec.Command(
 		dockerExe, "login",
@@ -86,6 +77,9 @@ func commandBuild(build Build, dryrun bool) *exec.Cmd {
 	for _, arg := range build.CacheFrom.Value() {
 		args = append(args, "--cache-from", arg)
 	}
+	for _, arg := range build.CacheTo.Value() {
+		args = append(args, "--cache-to", arg)
+	}
 	for _, arg := range build.ArgsEnv.Value() {
 		addProxyValue(&build, arg)
 	}