fixed `docker stop` to trigger clean shutdown for tt executable

[jens-ylja]

When using the Docker image to run ticktock I noticed docker stop to both take a long time and not cleanly terminating the ticktock executable. To verify the erroneous behaviour, please:

• docker run the origin Docker image with a mounted volume to have the logs outside the container
• tail -f the logfile
• docker stop the container
  • docker stop will hang for a while
  • the logfile will not contain the [INFO] [main] Shutdown process complete log
  • when restarting the container you maybe additionally will detect loss of data (old in-memory only data)

When drilling down this, the reason/solution was simple -> ticktock has to be run with exec in entrypoint.sh. For further explanation please see e.g. https://madflojo.medium.com/shutdown-signals-with-docker-entry-point-scripts-5e560f4e2d45.

This PR contains the according fix. To verify the fixed behaviour, please re-execute the procedure described above - you should now see the [INFO] [main] Shutdown process complete log message.

Note: The Dockerfile contains a STOPSIGNAL SIGINT statement which isn't really neded (for my opinion). Docker uses SIGTERM by default which in my tests seemed to work the same way.

[ytyou]

We registered the exact same handler for both SIGINT and SIGTERM, so yes, if Docker uses SIGTERM by default, then STOPSIGNAL SIGINT is not needed.

[jens-ylja]

We registered the exact same handler for both SIGINT and SIGTERM, so yes, if Docker uses SIGTERM by default, then STOPSIGNAL SIGINT is not needed.

OK, I'll update the PR on Monday - my todays working session is over.