Bump gatekeeper chart version to '3.7.0-bb.8'

Package Merge Request

Package Changes

Updated kubectl Docker tag to v1.21.5

Package MR

https://repo1.dso.mil/platform-one/big-bang/apps/core/policy/-/merge_requests/125

For Issue

Closes https://repo1.dso.mil/platform-one/big-bang/apps/core/policy/-/issues/150