Move snippets outside of markdown

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

docs/tests/core-concepts/container-images/plans/src/app.go

@@ -0,0 +1,7 @@
+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("Hello, 世界")
+}

docs/tests/core-concepts/container-images/plans/src/go.mod

@@ -0,0 +1,3 @@
+module dagger.io/test
+
+go 1.17