[documentation] Unify interface - provide resource_dict for Executor initialisation

[jan-janssen]

Currently the format on the Executor level and the submit() level are different, it would be great to unify both.

[jan-janssen]

This was achieved in #455 - still the documentation needs to be updated

[jan-janssen]

The resource dictionary is now explained in the documentation https://executorlib.readthedocs.io/en/latest/trouble_shooting.html#resource-dictionary