Motivation:

The organisations api can handle varieties of request. Since
this will evolve over time, integration tests are needed to
ensure that basic functionalities are not broken when a new
patch is submitted.

Modification:

- add various tests scenarios to cover all HTTP methods in the
    organisations API
- adjust the organisations controller:
    - post method to return 201, location url in the header
        and a json body that contain the newly create organisation
    - put method to return 200 if the uuid already exist or 201
        if it is a new uuid.
    - get, put and patch will first check the validity of the uuid
        and thrown and exception if the uuid is invalid.
    - change the return type of deleteUuid from void to long
- create CerebrumInvalidUuidException which will be use for invalid
    uuid
- add two exceptions to the CerebrumExceptionHandler which are
    CerebrumInvalidUuidException and HttpMessageNotReadableException
    (this is for malformed json or json+patch)
- add tests to check that CerebrumExceptionHandler handle those two
    new added exceptions
- fix some minor bugs inside CerebrumEntityUuidGenerator
- obtain and set aai token variable that will be use by the ci

Result:

Improve test coverage for organisation API and some minor
bug fixes.

Target: master
Acked-by: Franz Stephan
Review-at: https://gitlab.hzdr.de/hifis-technical-platform/helmholtz-cerebrum/-/merge_requests/20