Add .scalafmt

[aaabramov]

If we would like to support and enhance this library it would be nice to have common code style.
Moreover, Influx 2.0 is about to be GA (currently it is in Alpha), so there will be new features.

We can start from simplest cats config and improve it with the time.

• Add .scalafmt
• Add ci check for code formatting
• Add contribution notice about code formatting

[razem-io]

@aaabramov sounds good. I never really used .scalafmt because it was a problem with one of our devs. However it really makes sense because this is an open source project and we need to have some kind of contribution guide.
Do you like a code style config best?

[aaabramov]

I will make a PR with code style changes.

Also, @razem-io could you add me as a write member of this library so that I can contribute here directly instead of proposing changes via fork?

[razem-io]

@aaabramov perfect, thank you. I added you as a contributer.