Fix CORS headers not set on exceptions

[nielsbox]

Fixes #1820.
Correct error handling in response to CORS.

Changes proposed in this pull request:

• Add a MiddlewarePosition before Exception handling so CORS is always returned
• Add ServerError Middleware to handle unhandled errors between the ServerError- and ExceptionMiddleware
• Update corresponding docs

[coveralls]

coverage: 94.266% (-0.02%) from 94.287%
when pulling 918d58c on bugfix/cors-headers-on-exception
into bbd085b on main.

[RobbeSneyders]

Thanks @nielsbox!

This now returns different errors than the ExceptionMiddleware though. We probably want to align it:

connexion/connexion/middleware/exceptions.py

Lines 92 to 98 in bbd085b

	@staticmethod
	def common_error_handler(
	_request: StarletteRequest, exc: Exception
	) -> ConnexionResponse:
	"""Default handler for any unhandled Exception"""
	logger.error("%r", exc, exc_info=exc)
	return InternalServerError().to_problem()

[RobbeSneyders]

Thanks @nielsbox! Really clean.

I had some minor comments on the docs and the typing, so I quickly added commits handling those so I can merge and release.