text: Title: BaseConfig.multiindex_strict type hint
  Body: The [type hint for BaseConfig.multiindex_strict](https://github.com/unionai-oss/pandera/blob/3ea4f2c4a3a4443c13dd9741d35bb7c8cbb930ac/pandera/typing/config.py#L39) is currently `multiindex_strict: bool = False`.  However, because it allows "filter" as a value, I believe this type hint should be `Union[bool, str]`, similar to [BaseConfig.strict](https://github.com/unionai-oss/pandera/blob/3ea4f2c4a3a4443c13dd9741d35bb7c8cbb930ac/pandera/typing/config.py#L29).