Update Mattermost Instance to 5.32.1

Summary

New IB image is available: registry1.dso.mil/ironbank/opensource/mattermost/mattermost:5.32.1

Upstream doc on changes: https://docs.mattermost.com/administration/changelog.html

Should work on the existing operator version, otherwise wait for https://repo1.dso.mil/platform-one/big-bang/apps/collaboration-tools/mattermost-operator/-/issues/2 to be resolved.