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/alpine/alpine.cue

@@ -0,0 +1,36 @@
+// Base package for Alpine Linux
+package alpine
+
+import (
+	"alpha.dagger.io/dagger/op"
+)
+
+// Default Alpine version
+let defaultVersion = "3.15.0@sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3"
+
+// Base image for Alpine Linux
+#Image: {
+	// List of packages to install
+	package: [string]: true | false | string
+	// Alpine version to install
+	version: string | *defaultVersion
+
+	// Use of os package not possible : alpine is a low level component
+	#up: [
+		op.#FetchContainer & {
+			ref: "index.docker.io/alpine:\(version)"
+		},
+		for pkg, info in package {
+			if (info & true) != _|_ {
+				op.#Exec & {
+					args: ["apk", "add", "-U", "--no-cache", pkg]
+				}
+			}
+			if (info & string) != _|_ {
+				op.#Exec & {
+					args: ["apk", "add", "-U", "--no-cache", "\(pkg)\(info)"]
+				}
+			}
+		},
+	]
+}