MessageActions UI Customization

[ambaldwin]

Currently, there is not a way to override the default MessageActions UI dropdown as a whole or the individual 'action items' UI components within the list. Adding custom actions to the list as well as determining which of the actions are included in the list is possible. We're talking about the UI components here. Like, if they wanted to add an emoji or other text to each action item.

This issue has come up in support many times.

Goal: ability to override the MessageActions component and maybe the concept of overriding a not-currently-existing 'MessageActionItem' via a prop on Channel.