DataFrameSchema validation with multiple index options

[vladjohnson]

Describe the bug
We can only check one index type at a time. I would like to be able to check both datetime.datetime and int indexed dataframes.

• I have checked that this issue has not already been reported.

Code Sample, a copy-pastable example

    validation_schema: InstanceOf[pa.DataFrameSchema] = (
        pa.DataFrameSchema(
            {
                ".*": pa.Column(
                    float,
                    regex=True,
                    nullable=False,
                ),
            },
            index=pa.Index(datetime), # We would like to support both datetime and int
            unique_column_names=True,
        )
    )

Expected behavior

Validation schema that supports both int and datetime.datetime types.

Desktop (please complete the following information):

• OS: Linux Ubuntu 20.04
• Browser: Chrome
• Version: pandera==0.20.4