Addresses https://linear.app/comm/issue/ENG-9848/replace-quotes-with-markdown-quotes-in-sidebar-soucre-message and https://linear.app/comm/issue/ENG-9846/move-in-channel-channel-earlier-in-sidebar-source-message
In this diff, we replace the usage of quotations surrounding the cast text and replace it with markdown quotes by prepending > to each line of the original cast text.
The source message ordering is also rearranged with the channel text now accompanying the "author said" text which is then followed by the cast text.
Depends on D13865