Issue 395 first test

[c8y3]

This is a proposition to set up automatic tests for the REST API.
The tests are automatically run for every push with github actions.

Some notes:

• in order to ensure tests isolation (modification of the database by some test should not impact the results of another test), the docker-compose is started before each test and stopped after each, the volumes are pruned
• warning: running the tests will modify the .env at the root of the repository. It would be probably nicer to run the tests in an another directory (for instance tests/work_directory) or maybe a temporary directory. But to do that, it is necessary to copy the docker-compose and everything else needed to run in this directory. The current docker-compose makes this too complex. It would be nice to separate the build aspects from the run aspects of the docker-compose and also to try to minimize the number of dockers which are built ad-hoc...
• the same issue is seen again in the github actions.