gatekeeper update to 3.21.0-bb.0

Package Merge Request

Package Changes

https://repo1.dso.mil/big-bang/product/packages/policy/-/blob/3.21.0-bb.0/CHANGELOG.md

Package MR

big-bang/product/packages/policy!334 (merged)

For Issue

Closes big-bang/product/packages/policy#291

Upgrade Notices

N/A