FR: Provide "auto" compression also with "zstd", not only "zlib" and "lzma"

[tvogel]

The problem

The discussion here
borgbackup/borg#7054
quite clearly showed that even for zstd, using auto makes for a significant performance improvement and ultimately contributed to keeping the auto feature in borgbackup. So, it's unfortunate that I cannot easily select auto modes with zstd in Vorta.

Requested Solution

Adding the auto variants here should be easy and straight forward:

vorta/src/vorta/views/repo_tab.py

Line 45 in f1c7e92

self.repoCompression.addItem(self.tr('Zstandard Level 3 (modern)'), 'zstd,3')

Alternatives

In #1445, an alternative solution was proposed to add the "auto" option as a checkbox and the compression level as a slider.

Personally, I like the approach to limit the choices to a reasonable set of options. That's why I propose to just add auto,zstd,3 and auto,zstd,8. A little more context to make the decision easier would be helpful (e.g. links to compression benchmarks).

Using a checkbox (without mitigations) would allow people to make useless choices like auto,none or auto,lz4.

[madeddy]

The discussion here borgbackup/borg#7054 quite clearly showed that even for zstd, using auto makes for a significant performance improvement

Beats me why this is missing for zstd. A mistake?

Personally, I like the approach to limit the choices to a reasonable set of options.

I tend to agree. But to have so few compressions options, e.g. just two for zstd (3, 8) out of 0 to 22, is IMO strange at least, if not unlogical and not this bright.

Bottomline: "Auto" should absolutely be added and a few more spread out level options.