Add join types to Python dataframe

[Dandandan]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
The Python dataframe code only supports inner, left, right. But we have outer, semi too and a PR open for anti join.

https://github.com/apache/arrow-datafusion/blob/master/python/src/dataframe.rs#L146

Describe the solution you'd like
Add mapping for outer, semi and anti to the join types.

Describe alternatives you've considered

Additional context
It might be useful to implement FromStr for the enum for this?