Move policies to policies directory

[dyladan]

These should likely be moved to the new policies/ folder as well in a follow-up:

https://github.com/open-telemetry/community/blob/main/marketing-guidelines.md
https://github.com/open-telemetry/community/blob/main/social-media-guide.md
perhaps also
https://github.com/open-telemetry/community/blob/main/project-management.md

Originally posted by @arminru in #2819 (comment)