!so with a custom message format posts an empty message #722

Describe the bug
With a custom shoutout format, !so posts an empty message. FormatContent is called with msg, which is still "", instead of messageFormat:

The default format (no custom one) works.

To Reproduce
Call GiveShoutout with a non-empty message format: it returns "".

Expected behavior
helper.FormatContent(messageFormat, ...).

Additional context

• The placeholders documented in the TODO at

  monorepo/apps/twitch-bot/internal/command/so.go

  Line 39 in 35a83bd

  // TODO: Add this to web interface so streamers can customize their shoutout message format. The messageFormat can include placeholders like {streamer} {url} {game} which will be replaced with the actual streamer name, stream URL, and current game respectively.

  ({streamer} {url} {game}) aren't the ones FormatContent replaces ({twitch.username}, {twitch.url}, {stream.game}).
• go test ./twitchapi has 3 failing tests: TestGiveShoutout_DefaultMessage, TestGiveShoutout_CustomMessageFormat and TestGiveShoutout_UserNotFound (the last one panics at twitchapi_test.go:303). They still mock the /users endpoint that refactor: update logic in twitchapi GiveShoutout #636 stopped using.