Bugfix/fix-middleware-type-declaration

[Howard86]

• What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)

Bug fix: fix incorrect type declaration of NextApiRequestWithMiddleware

• What is the current behavior? (You can also link to an open issue here)

when using router.use, it will not allow to inject middleware type definition

• What is the new behavior (if this is a feature change)?

e.g. can use the following (optional)

type User = {
  name: string
}
router.use<User>(req => ({name: "USER"}))
router.get(req: NextApiRequestWithMiddleware<User> => req.middlware.name) 

• Other information: