Multiindex unique does not get passed in Schema model

Describe the bug A clear and concise description of what the bug is.

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☒ I have confirmed this bug exists on the latest version of pandera.
☒ (optional) I have confirmed this bug exists on the master branch of pandera.

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Code Sample, a copy-pastable example

import pandera as pa
from pandera.typing import Index, Series

class MultiIndexSchema(pa.SchemaModel):

    year: Index[int] = pa.Field(gt=2000, coerce=True)
    month: Index[int] = pa.Field(ge=1, le=12, coerce=True)
    passengers: Series[int]

    class Config:
        # provide multi index options in the config
        multiindex_name = "time"
        multiindex_strict = True
        multiindex_coerce = True
        multiindex_unique = True

index = MultiIndexSchema.to_schema().index

Expected behavior

I would expect SchemaModel and schema objects to have the same functionality, including for validation of multi index, including all the flags passed to the MultIndex class.

Desktop (please complete the following information):

OS: linux (ubuntu, rh8)
- Version: latest

Additional context

Ideally there should be a test that the features are the same. I'm happy to fix this bug (as it is a simple one-liner), but there probably should be more reflection on how to make sure that the features don't diverge between the 2 syntax. I will try to submit a PR, this is a great project, I hope I will be able to contribute in the future.

unionai-oss / pandera