Introduce plausibility check for outbound licenses
When creating a library or executable, several source files are combined into a binary artifact that has an outbound license of its own. This test generator allows to check if the combined source files are compatible with the desired outbound license.
Requirements for using these tests:
- input source files must contain the SPDX-License-Identifier tag
- python3 must be available
- the "reuse spdx" tool must be available