More contextual message variables

[merlinfuchs]

Original message: https://ptb.discord.com/channels/730045476459642900/1234983045598150677

Server:

• Server name ✅
• Server ID ✅
• Server icon URL ✅
• Server banner URL ✅
• Server guide banner URL
• Number of members ✅
• Number of online members

Boosts:

• Number of server boosts ✅
• Current server boost level ✅

Roles:

• Highest member role
• Total number of server roles
• Role that has been added / removed

Users:

• "me": User that has created the message on message.style

[merlinfuchs]

Some more message variables have been implemented as part of the new variable engine