improvement: improve discriminated union object naming

[armandobelardo]

A new configuration is introduced to make discriminated union member naming more Pythonic. With V1 union naming, member names change from <UnionName>_<DiscriminantValue> to <DiscriminantValue><UnionName>. Concretely, union members previously named Chat_User will now be named UserChat under the new configuration.

generators:
  - name: fernapi/fern-python-sdk
    config:
      pydantic_config:
        union_naming: "v1" # Other valid option is: "v0"

This also removes some of the old seed files within the python seed folder