add exclude pattern

[kay0u]

Problem

• We can't exclude files to the backup

Solution

• Add an option to ignore some folders

PR Status

• Code finished and ready to be reviewed/tested
• The fix/enhancement were manually tested (if applicable)

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[fflorent]

Shouldn't this feature be part of the yunohost backup create tool so it benefits to all backup methods?

Especially I feel like it would be confusing that the behaviour regarding .nobackup, since it already exists to exclude the data directories:
https://github.com/YunoHost/yunohost/blob/6388ef73c242aad86edd60bb05dfcd97733b97bc/hooks/backup/17-data_home#L33

[alexAubin]

Yes it should be part of the core, but the core's default backup is using .tar, and the corresponding python library has no straightforward way to "exclude" patterns (let's say you want to backup a folder A, but not the subdir A/B, etc..)

[fflorent]

OK then. Also it looks like it would be straightforward to generalize it when walking into the subdirectories is supported in the core.

[kay0u]

I'd be happy to generalize it, but the tarfile library used for the backup doesn't have this feature.