support for raw requests

[luolingchun]

Checklist:

• Run pytest tests and no failed.
• Run flake8 flask_openapi3 tests examples and no failed.
• Run mypy flask_openapi3 and no failed.
• Run mkdocs serve and no failed.

Regarding the idea of supporting raw requests, there is no data validation and support for OpenAPI UI.

from flask_openapi3 import OpenAPI
from flask_openapi3 import RawModel

app = OpenAPI(__name__)


class BookRaw(RawModel):
    mimetypes = ["text/csv", "application/json"]


@app.post("/book")
def get_book(raw: BookRaw):
    # raw equals to flask.request
    print(raw.data)
    print(raw.mimetype)
    return "ok"


if __name__ == "__main__":
    app.run(debug=True)