Update UserFlags to include Discord Certified Moderator

Created by: Lulalaby

Summary

Implements the following flag to DSharpPlus.User.UserFlags:

• DiscordCertifiedModerator

Details

Adds the following flag to the UserFlags enum.

• DiscordCertifiedModerator

Changes proposed

• Add DiscordCertifiedModerator with a value of 1<<18

Discord-API-Docs: https://github.com/discord/discord-api-docs/pull/2946 Data Mining: https://github.com/Discord-Datamining/Discord-Datamining/commit/6258cfefc7dde95d7c340397e9704c30da9a6280#commitcomment-50961513 This badge was internally already announced at the beginning of the year.