Obey gitattributes line endings when writing snapshots

[skuzzle]

Our current policy for line endings is: Snapshot serializers should produce system-independent line endings. This should, in theory to reproducible snapshots even on different systems.
There is an issue though when using git. Git has its own opinion about line endings on local machines. Depending on various settings, Git might convert line endings during checkout/checkin of files. This conversion might lead to unwanted failures during snapshot comparison.

As such, snapshot serializers should probably produce line endings in accordance to the local git repository settings.

Question remains whether we should introduce an extra dependency to handle the evaluation of git config or whether we want to implement it on our own.

See also: https://github.com/diffplug/spotless/blob/a92c7b04be4e2d1a896555c302505b903deae2fe/lib-extra/src/main/java/com/diffplug/spotless/extra/GitAttributesLineEndings.java#L65

[skuzzle]

Relates to #44