Git push notification in Chat view should truncate commit messages after the first paragraph

A common git commit message convention is to use the first line as a summary, followed by two newlines. Even if the summary isn't just a single line, though, it would still be a better experience to not drop the *entire* commit message into the Chat, leaving it to be truncated based on the width of my window. Instead, if the commit message is made up of multiple paragraphs (as separated by two newlines), then only the first one should be shown.

Locate the git push notification entry point in the Chat view and inspect how its commit message is displayed. Check messages containing multiple paragraphs separated by two newlines; done means the notification shows only the first paragraph instead of the entire commit message.

Written by the indexing model from the issue text.