Add validator and action payload for stepper

[GuessWhoSamFoo]

Validator and placeholder:

		fft := component.NewFormFieldText("textFormLabel", "textFormName", "")
		fft.AddValidator("placeholder", "this is an error", []string{"required"})

		form := component.Form{
			Fields: []component.FormField{
				fft,
			},
		}

		stepper := component.NewStepper("Test", "testAction")
		stepper.AddStep("Step1", form, "title1", "description1")
		stepper.AddStep("Step2", form, "title2", "description2")

Example message on submit with inputs of "test" and "test2" for "Step1" and "Step2" respectively:
{"type":"action.octant.dev/performAction","payload":{"action":"testAction","formGroup":{"Step1":{"textFormName":"test"},"Step2":{"textFormName":"test2"}}}}

Which issue(s) this PR fixes

• Fixes Support required form fields and error message #1291