Avoid .gitignore rewrite

[ascheman]

Is your feature request related to a problem? Please describe

I already have a well formed .gitignore in my root directory.
Nevertheless, mani sync adds it's own stuff to the .gitgnore file.

Describe the solution you'd like

I would like to be able to switch off (by default) the changes to the .gitignore, e.g. by adding an entry to the configuration file like adjust_gitignore (setting it to false, having true as the default).

[alajmo]

Good idea, will add it to the upcoming release.

[alajmo]

Added as of 0.30.0, you can either specify it via the config sync_gitignore: false or via a flag when syncing --sync_gitignore.