Allow doule indentation for function definitions

Many projects use double indentation for function definition arguments. That is in order to allow the arguments to be clearly separated and visible.

I have not found a configuraion/knob to allow this with yapf. No matter my config it always try to go only for single indentation. How could I make the following not be changed?

```diff
def create_oracle_cache(
- self,
- oracle: HistoricalPriceOracle,
- from_asset: AssetWithOracles,
- to_asset: AssetWithOracles,
- purge_old: bool,
+ self,
+ oracle: HistoricalPriceOracle,
+ from_asset: AssetWithOracles,
+ to_asset: AssetWithOracles,
+ purge_old: bool,
) -> None:
```

Keep in mind the double indentation is **only** for function definitions. Everywhere else it should be single.

Related issue but still no solution: https://github.com/google/yapf/issues/843