feat: provide loading indicator when retrying to send a message

[MartinCupela]

Motivation

When re-sending message is in progress a (loading) placeholder / indicator should be provided for the message bubble. Otherwise the message is unmounted what leads to blinking.

missing_loading_indicator_message_resend.webm

Acceptance Criteria

The message bubble is kept mounted The message bubble reflects the fact that the message sending is in progress