Allow excluding directories from local backup

[Gchbg]

Is your feature request related to a problem? Please describe.

My AIO instance has limited storage. When my files are backed up locally by the borg system, my effective storage is halved. Some of my data can be regenerated if lost, or is otherwise not critical, and I would like to exlude it from backup.

Describe the solution you'd like

I would love to have an easy way to exclude certain directories from all backups. This can be easily achieved by adding two command-line options to the borg create invocation in the aio-borgbackup container: --exclude-if-present=.noaiobackup --keep-exclude-tags. This will exclude any directory which contains a file called .noaiobackup within it.

In this way, I can exclude directories with non-critical data from my backups, reducing the storage requirement for my local backup, and making more of my limited storage available for actual data.

I've been using this solution on a locally modified AIO instance without issues.

Additional context

This change is trivial and completely backward-compatible. People who do not have .noaiobackup files will not experience any difference.

[szaimen]

Hi, interesting idea! Just to make it clear directly, I will not work on this but would accept a PR that adds this feature.

Please make sure that the restore with rsync also respects these files then so that it will not delete all the folders that contain these files when you try to do a restore from the AIO interface.