Add data type "DateTimeUtc"

[BirgitBoss]

closes #498

• bugfix negative integer example

[BirgitBoss]

@s-heppner should be conformant to what is already implemented in schema, correct?

[s-heppner]

As far as I can see, it would not change the resulting schema files, however it will need adaption of aas-core-meta with the new type.

Edit: After some more detailed looking into the code, I think the changes would only be editorial and backward compatible, as long as the only two attributes that should have this type are Event/lastUpdate and Event/timestamp.