Add sql-formatter hook

[slyapustin]

There is an unofficial hook for sql-formatter which might be added to the list.

Was trying to convince the author to add an official integration, but he is against it.

[asottile]

I don't know what you want me to do about it -- the author seems to ignore tools like eslint or rubocop which are orders of magnitude more popular than their tool which have set up an integration

[slyapustin]

I would like to have an alternative for sqlfluff (which is insanely slow on big SQL files) in the list https://pre-commit.com/hooks.html

sql-formatter is a nice alternative for that, and I added an integration for it: https://github.com/slyapustin/pre-commit-sql-formatter