Move core actions to a subpackage

Signed-off-by: Helder Correia <174525+helderco@users.noreply.github.com>

tests/plan/client/env/usage.cue

@@ -2,6 +2,7 @@ package main
 
 import (
 	"dagger.io/dagger"
+	"dagger.io/dagger/core"
 )
 
 dagger.#Plan & {
@@ -10,15 +11,15 @@ dagger.#Plan & {
 		TEST_SECRET: dagger.#Secret
 	}
 	actions: {
-		image: dagger.#Pull & {
+		image: core.#Pull & {
 			source: "alpine:3.15.0@sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3"
 		}
 		test: {
-			string: dagger.#Exec & {
+			string: core.#Exec & {
 				input: image.output
 				args: ["test", client.env.TEST_STRING, "=", "foo"]
 			}
-			secret: dagger.#Exec & {
+			secret: core.#Exec & {
 				input: image.output
 				mounts: secret: {
 					dest:     "/run/secrets/test"