Add option to also load/modify Welcome chat message

[germanocaumo]

Would be nice to be able to fetch and then modify the Welcome chat message, currently
useLoadedChatMessages don't return the welcome chat message.

[GuiLeme]

This issue is still necessary, even though the place we find the welcome message changed.

Perhaps a new hook to fetch this dom element would be called:

useWelcomeMessageDomElement

Do we agree on the name?