How do I provide example values for PaginationParameterSchema?

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I really like adding example data to my OpenAPI spec. It helps some of my users understand my API endpoints more easily, and Rapidoc UI has a convenient "Fill Example" button to autofill example data when playing with the API interactively.

In general, I can add the `example=` or `examples=` keyword arguments to blueprint decorators to provide OpenAPI example data for parameters, return values, etc. I've also noticed that I can put these keywords in the `marshmallow.field()` definition to get the same effect. However, I can't find a way to specify example values for the automatic paging parameters added with the `Blueprint.paginate` decorator. The decorator itself doesn't expose a `**kwargs` parameter, and the schema of the generated object is created on the fly in a private helper function.

So far, the only way I've found to add examples to these values is by subclassing Blueprint, copy/pasting both `paginate` and the helper function `_pagination_parameters_schema_factory`, and adding example values to the anonymous class in that helper, like this:

```python
def _pagination_parameters_schema_factory(def_page, def_page_size, def_max_page_size):
"""Generate a PaginationParametersSchema"""

class PaginationParametersSchema(ma.Schema):
"""Deserializes pagination params into PaginationParameters"""

class Meta:
ordered = True
unknown = ma.EXCLUDE

page = ma.fields.Integer(
load_default=def_page,
validate=ma.validate.Range(min=1),
example=def_page, # Use the default page parameter as an example value
)
page_size = ma.fields.Integer(
load_default=def_page_size,
validate=ma.validate.Range(min=1, max=def_max_page_size),
example=def_page_size, # Again, use the provided default as an example
)

@ma.post_load
def make_paginator(self, data, **kwargs):
return PaginationParameters(**data)

return PaginationParametersSchema
```

I'm opening this as an issue rather than just submitting a PR for that change because I'm new to flask-smorest and Marshmallow, and I could just be missing something obvious. This seems similar to #327, but not identical.

Is there an easier / better way to provide example data for these pagination fields?

Start with the Blueprint.paginate decorator and the private _pagination_parameters_schema_factory helper described in the issue. Trace how the generated PaginationParametersSchema reaches the OpenAPI output, then check existing pagination and schema tests. Done means there is a supported way to provide example values for the generated page and page_size parameters without subclassing Blueprint.

Written by the indexing model from the issue text.