Consider adding (*adaptivecard.Message).AddElement method

[atc0005]

The method would add the given Element to the first card in the collection or an error if a Card is not already present.

The current alternatives:

msg, err := adaptivecard.NewSimpleMessage(msgText, msgTitle, true)
if err != nil {
	// ...
}

// element := ...
msg.Attachments[0].Content.Body = append(
	msg.Attachments[0].Content.Body,
	element,
)

or:

msg, err := adaptivecard.NewSimpleMessage(msgText, msgTitle, true)
if err != nil {
	// ...
}

// element := ...
msg.Attachments[0].Content.AddElement(false, element)

Because of the adaptivecard.NewSimpleMessage call we already know that a Card in msg.Attachments is present. While this allows us to safely take either of these approaches to add a new element to the first Card, it's not exactly ergonomic to do so.

Providing an AddElement method for the Message value would presumably make this scenario easier to work with.