This adds a new `DiscordMessageAttachment` type which is part of
`DiscordMessage`. Along with that type, there's also a new database
table for `discord_message_attachments` and corresponding persistence
APIs.
This commit also changes how chat messages are retrieved.
Here's why:
`DiscordMessage` can have multiple `DiscordMessageAttachment`.
A chat message can have a `DiscordMessage`.
Because we're `LEFT JOIN`'ing the discord message attachments into the
chat messages, there's a possibility of multiple rows per message.
Hence, this commit ensures we collect queried discord message
attachments on chat messages.
* add PinMessage and PinnedMessage
* fix gruop pin messages
* add SkipGroupMessageWrap to pin messages
* update pinMessage ID generation to be symmetric
Pascal Precht
Andrea Franz