Automatically link/format labels, users/teams, etc

[alystair]

Right now Yappy does not do anything special with comments. I believe they should be formatted and linked. This could be improved using some regex:

• Labels
  ~"LABEL_TEXT" links to https://<DOMAIN>/<REPO_PATH>/-/issues?label_name=<LABEL_TEXT>. Labels can contain emojis. Strip ~"". Unsure how much customization Discord allows but webhook returns label color in hex, description (for title popup?), among other things.
• Users/Teams
  @TEXT links to https://<DOMAIN>/<LABEL_TEXT>
• Weight (issue only)
  If available could be listed next to title with :scales: ⚖ icon

Must ignore:

• All text wrapped in ``` and ` (backtick contexts)
• @all (entire team)

More details about formatting and additional types here: https://docs.gitlab.com/ee/user/markdown.html#special-gitlab-references