refactor!: Move image definitions to dagger/core

BREAKING CHANGE: Adjust imports for for `#Ref`, `#ImageConfig` and `#HealthCheck`.

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

pkg/universe.dagger.io/docker/image.cue

@@ -2,6 +2,7 @@ package docker
 
 import (
 	"dagger.io/dagger"
+	"dagger.io/dagger/core"
 )
 
 // A container image
@@ -10,7 +11,7 @@ import (
 	rootfs: dagger.#FS
 
 	// Image config
-	config: dagger.#ImageConfig
+	config: core.#ImageConfig
 }
 
 // A ref is an address for a remote container image
@@ -20,4 +21,4 @@ import (
 //   - "index.docker.io/dagger:latest"
 //   - "index.docker.io/dagger:latest@sha256:a89cb097693dd354de598d279c304a1c73ee550fbfff6d9ee515568e0c749cfe"
 // FIXME: add formatting constraints
-#Ref: dagger.#Ref
+#Ref: core.#Ref

pkg/universe.dagger.io/docker/set.cue

@@ -1,7 +1,6 @@
 package docker
 
 import (
-	"dagger.io/dagger"
 	"dagger.io/dagger/core"
 )
 
@@ -11,7 +10,7 @@ import (
 	input: #Image
 
 	// The image config to change
-	config: dagger.#ImageConfig
+	config: core.#ImageConfig
 
 	_set: core.#Set & {
 		"input":  input.config