Add an example of updating modal

[KouWakai]

Hi!! I added updating modal example

since I wanted to know how could I handle updating modal in examples.

[KouWakai]

Thank you for feedback:pray:
I would modify codes to the suggestion

[charlesoconor]

I couldn't get api.UpdateView to work under this event. I had to use slack.InteractionTypeBlockActions e.g block_action. Is this working for you?

[KouWakai]

Thank you for the feedback,I would check that.

[KouWakai]

It's working but modal closes right after update.

I think this is caused by slack server.
after update modal,app respond http status 200 to slack server and the server see it as over

I'v been running this code on local and connect via ngrok and this happen

[KouWakai]

by adding time.Sleep(time.Second * 2) after api.UpdateView you can prevent sending http 200 and can see updated modal.

	case slack.InteractionTypeViewSubmission:
		//you can use any modal you want to show to users just like creating modal.
		updateModal := updateModal()
		// You must set one of external_id or view_id and you can use hash for avoiding race condition.
		// More details: https://api.slack.com/surfaces/modals/using#updating_apis
		_, err := api.UpdateView(updateModal, "", i.View.Hash, i.View.ID)
		time.Sleep(time.Second * 2)
		if err != nil {
			fmt.Printf("Error updating view: %s", err)
			w.WriteHeader(http.StatusInternalServerError)
			return
		}

[KouWakai]

@kanata2 @charlesoconor
sorry for kept you waiting,could you review this code?

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[github-actions]

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[parsley42]

Even if this example isn't perfect, it's an expansion of what we had before.