Allow null on allowReserved and allowEmptyValue properties

[snoob]

Q	A
Branch?	4.1
Tickets	Closes #7220
License	MIT
Doc PR	N/A

As discussed here: #7220, the Swagger specification now restricts the use of allowReserved and allowEmptyValue (see https://swagger.io/specification).

allowReserved only applies to parameters with an in value of query
allowEmptyValue is valid only for query parameters
Using it on a path or header parameter is deprecated.

By default, ApiPlatform sets both properties to false regardless of the parameter type. The workaround is to set it to null instead so that it is not generated in the schema.

The purpose of this merge request is to allow null as a valid value for these two properties.

[soyuka]

Thanks! It'd be nice to fix the constructor on the main branch and use null as default value. At least we should set null according to the parameter type.

[snoob]

@soyuka i wanted to create a MR but it's already null on main branch.

I compared the properties and getter/canner with the main branch and i realized that i probably forgot to update the return type for this methods on 4.1.. Sorry for that

#7322