Added indent with indicators to yaml-v12

[aheiska]

Enables to indent yaml like:

root:
  - item1
  - item2

This applies only to circe-yaml-v12. I could not come up with a way to do it for circe-yaml in a binary compatible way (I would assume this is binary compatible).

Test copied from https://github.com/circe/circe-yaml/pull/398 and implemented PrinterBuilder builder as suggested there.

I also added deprecations. Values are just a guess and maintainers can of course change then as they see fit.