Add git.#Commit definition and git.#Image

This definition allow user to commit & push new content to repository.
I've also add a quick feature to os.#Container to write files.

Signed-off-by: Tom Chauveau <tom.chauveau@epitech.eu>

stdlib/git/image.cue

@@ -0,0 +1,11 @@
+package git
+
+import (
+	"alpha.dagger.io/alpine"
+)
+
+#Image: alpine.#Image & {
+	package: {
+		git: true
+	}
+}