cue modules: move stdlib to pkg/alpha.dagger.io

In preparation for Europa, we will vendor multiple CUE modules:

- `pkg/alpha.dagger.io`: legacy non-europa packages
- `pkg/dagger.io`: core Europa packages
- `pkg/universe.dagger.io`: Europa universe

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

pkg/alpha.dagger.io/gcp/gcr/gcr.cue

@@ -0,0 +1,47 @@
+// Google Container Registry
+package gcr
+
+import (
+	"alpha.dagger.io/dagger/op"
+	"alpha.dagger.io/gcp"
+)
+
+// Credentials retriever for GCR
+#Credentials: {
+	// GCP Config
+	config: gcp.#Config
+
+	// GCR registry username
+	username: "oauth2accesstoken" @dagger(output)
+
+	// GCR registry secret
+	secret: {
+		string
+
+		#up: [
+			op.#Load & {
+				from: gcp.#GCloud & {
+					"config": config
+				}
+			},
+			op.#Exec & {
+				always: true
+				args: [
+					"/bin/bash",
+					"--noprofile",
+					"--norc",
+					"-eo",
+					"pipefail",
+					"-c",
+					#"""
+						printf $(gcloud auth print-access-token) > /token.txt
+						"""#,
+				]
+			},
+
+			op.#Export & {
+				source: "/token.txt"
+			},
+		]
+	} @dagger(output)
+}