Greatly increase text limits for Verified/Partner server Announcement channels

I'm a game developer, and we use our Discord super heavily for things like announcing patches. We like to duplicate patchnotes for easy reading in Discord instead of going to our readme site. 

However, our patch notes _always_ exceed 2000 characters.

Partner/Verified servers that use announcement channels for users to follow should have the text limit greatly increased (say, from 2000 to 10k).