mattermostOperator update to 1.20.0-bb.0

Package Merge Request

Package Changes

https://repo1.dso.mil/big-bang/product/packages/mattermost-operator/-/blob/1.20.0-bb.0/CHANGELOG.md

Package MR

big-bang/product/packages/mattermost-operator!48 (merged)

For Issue

Closes big-bang/product/packages/mattermost-operator#26 (closed)