Add ability to insert user-visible or user-hidden messages into the chat

[ataibarkai]

Is your feature request related to a problem? Please describe.
Programmatically insert user-visible and user-hidden messages into the chat

Describe the solution you'd like
Probably a hook that makes available a insertMessage function.

Describe alternatives you've considered
Hook that makes it possible to edit messages altogether (e.g. editMesasges: Message[] -> Message[])
with insertMessage as a specialization

Additional context
E.g. to help with this request on discord