Refactor parameters resolution and merging

Making the parameter resolution reusable by install/upgrade and inspect
in the future.

Signed-off-by: Djordje Lukic <djordje.lukic@docker.com>

Author: rumpl

cmd/docker-app/parameters_test.go

@@ -12,7 +12,8 @@ import (
 func TestWithLoadFiles(t *testing.T) {
 	tmpDir := fs.NewDir(t,
 		t.Name(),
-		fs.WithFile("params.yaml", `
+		fs.WithFile("params.yaml",
+			`
 param1:
   param2: value1
 param3: 3