[MAINTENANCE] Update crystal version to latest

[kosstennbl]

For a long time crystal version for which this project is intended wasn't changed from 1.6.2 (current latest is 1.13.3).

This issue was discussed, but update was postponed due to issues with Ameba #1814 #1811

After Ameba would be removed (as a part of #2157), updating crystal should be a straightforward process without additional hinderances. Because of that, #2157 would be a prerequisite for this issue.

Crystal update means several things:

• Update crystal version and build image from tools/github-runner/Dockerfile. Upload it to dockerhub
• Update CI to use new version of the image
• Run CI tests to ensure that everything works properly on new crystal version
• Update documentation