Show only one notification for all new messages on Android instead of one per message

Keybase is the only instant messaging app I am aware of that shows a new notification per new message. This yields to having on a sudden 30 new notifications, which is unusable and lead me to turning off keybase notifications completely for now. Please consider aggregating to one notification that contains information like "Person X sent Y messages" -- for good solutions check out Signal or Conversations.

Start by locating the Android notification handling for new chat messages. Reproduce the issue with many incoming messages and compare the current per-message behavior with the requested single aggregated notification containing the sender and message count. Done means new messages produce one usable notification rather than a separate notification for each message.

Written by the indexing model from the issue text.