add gx ontology and gx shacl shapes

[robertschubert]

Description

added gx ontology and shacl shapes. Readme was added where we describe the source of the files as well as necessary changes of the files.

Type of change

Please delete options that are not relevant.

• [x] New type (non-breaking change which adds a type)
• [ ] Change (non-breaking change or fix on an existing type)
• [ ] Breaking change (Change that would cause existing Self Descriptions not to be accepted anymore by a Federated Catalogue)

How Has This Been Tested?

There was a manual process in the past. This is replaced by this programatic and documented approach.

[jdsika]

@heuerfin , @jtdemer , @MircoNierenz and @rcrswld this can be used by you after merge!

[jdsika]

Thank you Robert for your work!