feat(refacto): move everything in internal package

This allows to install katenary with `go install` and to clean up the
project folder.

internal/generator/labels/labelstructs/mapenv.go

@@ -0,0 +1,14 @@
+package labelstructs
+
+import "gopkg.in/yaml.v3"
+
+type MapEnv map[string]string
+
+// MapEnvFrom returns a MapEnv from the given string.
+func MapEnvFrom(data string) (MapEnv, error) {
+	var mapping MapEnv
+	if err := yaml.Unmarshal([]byte(data), &mapping); err != nil {
+		return nil, err
+	}
+	return mapping, nil
+}