mattermost update to 11.4.2-bb.1

Package Merge Request

Package Changes

https://repo1.dso.mil/big-bang/product/packages/mattermost/-/blob/11.4.2-bb.1/CHANGELOG.md

Package MR

big-bang/product/packages/mattermost!353 (merged)

For Issue

(not closing because there are some manual release note updates that need to be made)

big-bang/product/packages/mattermost#255 (closed)

Upgrade Notices

If using the Mattermost-provided Postgresql in-cluster sub-chart database, you will be required to perform a pg_dump before upgrading. Then, you will need to restore the database using pg_restore to the updated postgresql pod. This in-cluster, sub-chart database is NOT a production setup/recommended installation. Documentation and other changes can be found here: https://www.postgresql.org/docs/18/release-18.html#RELEASE-18-MIGRATION