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>

cmd/docker-buildx/config.go

@@ -183,6 +183,12 @@ func settingsFlags(settings *plugin.Settings) []cli.Flag {
 			Usage:       "sets images to consider as cache sources",
 			Destination: &settings.Build.CacheFrom,
 		},
+		&cli.StringSliceFlag{
+			Name:        "cache-to",
+			EnvVars:     []string{"PLUGIN_CACHE_TO"},
+			Usage:       "cache destination for the build cache",
+			Destination: &settings.Build.CacheTo,
+		},
 		&cli.BoolFlag{
 			Name:        "pull-image",
 			EnvVars:     []string{"PLUGIN_PULL_IMAGE"},