Add support of optional parameters in NilPortugues\Api\JsonApi\Server\Actions\CreateResource

[GSokol]

Some parameters could:

• be null
• have default value
• be set by client or counted by server (like nickname from first name, last name and year of birth)

[nilportugues]

@GSokol

This can be solved already, but code needs to be added in place before release.

See https://github.com/nilportugues/php-json-api/commit/490b15f0a346ac989cf8e102d3aec2d2a1f059e3

Need to finish this release to allow this behaviour.

[GSokol]

Ok. Waiting for release.

[GSokol]

@nilportugues why could not be an object without required properties? (I mean, if we use NilPortugues\Api\Mapping\Mapping, created from symfony-jsonapi bundle by yamls)