[Suggestion] Don't prune manual backups

[Minecraftschurli]

Backups triggered manually could be marked in the name and excluded from pruning if option is set.

[itzg]

That's a great idea.

If someone wants to contribute a PR then that would be very helpful. It would involve enhancing the calls like

docker-mc-backup/scripts/opt/backup-loop.sh

Line 230 in aea603f

find "${DEST_DIR}" -maxdepth 1 -name "*.${backup_extension}" -mtime "+${PRUNE_BACKUPS_DAYS}" "${@}"