Merge branch 'nkupdates' into 'main'

Dockerfile

docker_release_version.sh

tests/docker-compose.yml.mysql.tmpl

tests/docker-compose.yml.postgresql.tmpl

tests/run-cluster-test

usr/local/bin/start-mattermost-jobserver

usr/local/bin/start-mattermost-server

...flexible-docker-containers/healthcheck.d/44-mattermost.sh

.../share/flexible-docker-containers/init.d/44-mattermost.sh

...share/flexible-docker-containers/tests.d/44-mattermost.sh

...share/flexible-docker-containers/tests.d/99-mattermost.sh