OpenBrush Third Grant(follow up 2) (#921)

* Follow up 2 Grant for OpenBrush with 6-9 milestones

* Split milestones into 6-7, 8-9. Removed `set_code_hash` part. Reduced rate to fit < 100 000

* Update openbrush-follow-up-2.md

* Update openbrush-follow-up-2.md

Co-authored-by: xgreenx <[email protected]>

Author: TtomaS7