Consider moving sqlite file outside of repository

[dmpetrov]

I have heard a few times that people don't like the idea of using binary DB files in DVC and storing them in Git repo. One guy even stopped looking at DVC when he realized this (misunderstood, actually) . The other folks think that DVC requires DB and uses sqlite by default.

The misunderstandings are not an issue. However, it makes people think that DVC has a bad design that might introduce bad practices in their workflow and prevents them from using DVC.

To make DVC design decisions clear we can consider moving .dvc/state file (sqlite) outside of repo - somewhere to /var. I understand that it might require some additional work on naming these files properly. Another, easy solution might be a proper file naming like .dvc/ephemeral.state or .dvc/state.tmp.

[efiop]

@dmpetrov Interesting observation! Maybe let's move it to .dvc/tmp/state? We have .dvc/tmp dir already and a using it for some temp files, so maybe that will make them much less noticeable.

[efiop]

Closing in favor of #3666