ops: set default PLATFORMS var to local platform

docker-bake.hcl

@@ -29,7 +29,7 @@ variable "PLATFORMS" {
   // Only a specify a single platform when `--load` ing into docker.
   // Multi-platform is supported when outputting to disk or pushing to a registry.
   // Multi-platform builds can be tested locally with:  --set="*.output=type=image,push=false"
-  default = "linux/amd64"
+  default = "${BAKE_LOCAL_PLATFORM}"
 }
 
 // Each of the services can have a customized version, but defaults to the global specified version.