Aas-core3.0

This is the first stable release. The release candidates stood
the test of time, so we are now confident to publish a stable
version.

In this version, we fix:

* Constraints AASc-3a-010 and AASd-131, propagated from aas-core-meta pull requests 281 and 280, respectively.

We also add the following minor feature:

* Add ``__repr__`` to ``verification.Error`` to facilitate debugging in the downstream clients. Propagated from aas-core-codegen pull request 400.

* Update to aas-core-meta, codegen, testgen 44756fb, 607f65c,
bf3720d7 (7)

* This is an important patch propagating in particular the following fixes
which affected the constraints and their documentation:

* Pull requests in aas-core-meta 271, 272 and 273 which affect the
nullability checks in constraints,

* Pull request in aas-core-meta 275 which affects the documentation
of many constraints.