fix(metadata): use operation output class for mapping instead of operation class

[Spomky]

Q	A
Branch?	4.2
Tickets	Closes #7593
License	MIT
Doc PR	not needed

As shown in #7593, the output class is not used when the Object Mapper is enabled. It appears that the ObjectMapperProvider always relies on the resource class instead. This PR fixes the issue in the same way it is already handled in ObjectMapperProcessor.

[Spomky]

~Please wait before merging this PR. There is another issue now and I cannot figure out why. The @id is now /.well-known/genid/[hex value] instead of the correct resource IRI. Not sure why...~

[soyuka]

thanks!