Updating to v3.0RC02

[mjacoby]

This PR collects changes, issues and ToDos related to updating to v3.0RC02.

• Enum Naming
  Enum names for serialization are currently being generated rule-based. If possible, shall become constant, i.e. being provided as part of the input to the model generator and stored in the generated Enum classes.
  Until this is available, generated names will be used.
• Update handling of embeddedDataSpecifications (see Enable more than one DataSpecificationContent #14)
  Currently we expect the following format

       "embeddedDataSpecifications": [
           "embeddedDataSpecifications": {...},	// reference indicating the type
           "dataSpecificationContent": {...}		// actual data specification
       ]
  

  In the future, either embeddedDataSpecifications or dataSpecificationContent should be present.
  However, it is still undefined how the actual (sub-)type of dataSpecificationContent should be serialized, so this cannot be implemented right now.
  Therefore, this functionality is currently disabled until standardization progresses.
• ...

[mjacoby]

1. Inversing the makePlural algorithm (https://github.com/eclipse-aas4j/aas4j-model-generator/blob/main/aas/src/templates/to_plural_form.rq) seems to be straight forward if I'm not missing something. Only problem might occur if have have words that end in 's' in singular because then we can't know if the 's' at the end is a plural 's' or part of the word itself.
   If we do have such words, we have a problem and would require some additional mapping file for mapping between singular and plural...

2. Not a blocker from my perspective. We can fix this in the final release.

3. Regarding enums - right now we have an inconsistency as one enum element exists twice in our model and those instances are not the same or equals - this might cause problems in de-/serializing. But I'm fine with keeping it as-is until a concrete problem with it arises.

[mjacoby]

I just updated dataformat-core and dataformat-json and this seems fine and working now.
However, I removed the support for custom DataSpecificationContent implementation as it is unclear is they are allowed and how they should be handled with latest changes regarding serialization of embeddedDataSpecification. This causes dataformat-xml to break. However, dataformat-xml does not seem like it has been updated to v3.0RC02 as there is e.g. no support for SubmodelElementList. Also the unit tests have been deactivated for dataformat-xml and when actived some of them failed. Not sure if we lost something while merging or it has never been implemented.
Additionally, some files are damaged due to incorrect merging, e.g.

aas4j/dataformat-xml/src/test/resources/test_demo_full_example.xml

Line 725 in 1a76a01

<<<<<<< HEAD

I now consider dataformat-core and dataformat-json basically ready and would appreciate a review.

[FrankSchnicke]

After #48 is merged we can also merge this PR.

[sebbader-sap]

I have just changed the state of this PR from draft to ready for review. I am personally not 'ready for review' (too many hours in front of the monitor) but will have a look again tomorrow. Would be great if you guys can also add your opinion here before we decide to merge it.

[sebbader-sap]

• fix the error in the build pipeline: https://github.com/eclipse-aas4j/aas4j/actions/runs/3631146430/jobs/6125385007
• fix the AASX bugs (issue Fix AASX Unit Tests #5)