Updated mattermost-operator with securityContext support

Package Merge Request

Package Changes

https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost-operator/-/blob/1.18.0-bb.1/CHANGELOG.md

Package MR

https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost-operator/-/merge_requests/40

For Issue

Closes https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost-operator/-/issues/19