Update docker.io/mongo Docker tag to v8

Successfully upgraded the Docker container on the Database Host using Watchtower infrastructure.

Prior to this procedure, the migration was done by using the tools mongodump and mongorestore like this:

docker exec bierochs-mongo sh -c 'exec mongodump --uri="mongodb://mongodb.bierochs.org:27017/" -d rocketchat --archive' > /srv/mongodb8/data/dump/rocketchat.archive
docker exec bierochs-mongo8 sh -c 'exec mongorestore --username=****** --password=******  --uri="mongodb://mongodb.bierochs.org:27018/" --archive=/data/dump/rocketchat.archive'

This MR contains the following updates:

Release Notes