Add configurability feature to the catalogue

We identified the need for more configurability of the catalogue for different features. Currently the only supported configurability feature is provided for the /verification frontend. Here, it is configurable which of the aspects semantics, schema, and signature should be considered during the verification process. Such configurable parameters should also be made available for the following features:

1. What types of self descriptions the catalogue accepts (see #173). E.g., for some use cases it might be important to be able to upload data asset self descriptions indepentently, while in other use cases it might be helpful to enforce a direct link to a service offering
2. Verifying signatures in the uploading process (see #179 (closed)). To use the catalogue locally it might be helpful to disable the check of the signatures of the self description when uploading it to the catalogue

This is an overarching issue for the need of configurability and the list above might be extended by further sub-issues when further need for configurability of a feature is identified.