Update Mattermost to 7.1.2

Package Merge Request

Package Changes

https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost/-/blob/7.1.2-bb.0/CHANGELOG.md

Package MR

https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost/-/merge_requests/95

For Issue

Closes https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost/-/issues/53