Allow processing of multiple metadata resource in OMI

[jh-RLI]

Description of the issue

Currently, OMI can only validate oemetadata documents that include a single resource object. Since oemetadata v2 we restructured the metadata which makes it necessary to be able to validate multiple resources as one dataset can include multiple.

Solution

• Check how to adapt this for v2, but keep it consistent with v1

https://github.com/OpenEnergyPlatform/omi/blob/e05937f61d7104d3a5ae29e09cc9b4fbb3d5fae4/src/omi/validation.py#L501C5-L501C39

Workflow checklist

• I am aware of the workflow in CONTRIBUTING.md