Handle recaptchas when sending messages

[Schmiddiii]

Sometimes one gets rate-limited when sending a message. presage should handle such cases and notify downstream applications that the user will need to submit a recaptcha and afterwards presage should retry sending the message.

Currently, once one gets an error when sending the message, and the message that should have been sent is lost forever.

Some design proposed by @gferon would be returning a future that could be polled and which can be used to re-send the message.

I would have proposed to store the message somewhere in the store and have a function to resend all failed messages. This would also help in cases where one sends messages without an internet connection (which Flare currently prevents, but I am sure one could race this and could happen either way). Another thing that may help (but which would require much greater changes) is to make the receive-message stream not only return messages but also status updates (in this case "please fill out captcha") instead of returning an error when sending a message (in this case it would be fine to return "Ok" as the message will be sent later).

Downstream issue on Flare: https://gitlab.com/Schmiddiii/flare/-/issues/81.