Sanity checks for Stork 1.6.0 rc1

We are now at step SANITY CHECKS of Stork 1.6.0 rc1.

Please do sanity checks according to the steps below:

1. Get the tarball and check it, run tests with rake unittest:backend or rake unittest:backend_db.
2. Get the deb & rpm packages, place them in the tarball location, run tests with rake system_tests and rake system_tests_ui.
3. Start demo locally with rake demo:up and follow the steps from the demo wiki: https://gitlab.isc.org/isc-projects/stork/-/wikis/Demo
4. Install server and agent locally e.g. in VMs from deb & rpm packages

Before starting, please state what you are checking in a thread/discussion (not as comment).

When you finish a check, state in the same thread/discussion what the result is. This way we know what is covered upfront and we can avoid repeating ourselves.

* tarball: https://gitlab.isc.org/isc-projects/stork/-/jobs/2740406/artifacts/browse
* apk & deb & rpm packages: https://gitlab.isc.org/isc-projects/stork/-/jobs/2740410/artifacts/browse