add missing user_dir to finetunning config

[orena1]

What does this PR do?

user_dir: ${env:PWD}/examples/data2vec is missing in the finetunings configs, without this config the data2vec models are not registered (here) to TASK_DATACLASS_REGISTRY and the model can not be loaded.

Did you have fun?

:) I did :) very flexible code :-o

I think it is related to @alexeib