mattermost update to 11.3.0-bb.0

Package Merge Request

Package Changes

https://repo1.dso.mil/big-bang/product/packages/mattermost/-/blob/11.3.0-bb.0/CHANGELOG.md

Package MR

big-bang/product/packages/mattermost!344 (merged)

For Issue

Closes big-bang/product/packages/mattermost#248 (closed)

Upgrade Notices

N/A