Explore OQ Engine >> 3.11 and set up CI tests

[anthonyfok]

Current release of OpenDRR/earthquake-scenarios (as of v1.2.3) has been tested/certified to work with only OpenQuake Engine 3.11.5.

As we'll need to upgrade to a newer version of OQ Engine (such as the latest 3.18.0 release) eventually, it would be a good idea to start exploring getting OpenDRR/earthquake-scenarios to work with OQ Engine >> 3.11.

• Update our code to be compatible with OQ Engine >= 3.11.5
• Set up CI tests (with a GitHub Actions workflow) for multiple OQ Engine releases (e.g. 3.11.5, 3.12.1, 3.13.0, 3.14.0, 3.15.0, 3.16.7, 3.17.1, 3.18.0) and compare their calculation results
• Update documentation, especially Python version requirement for different OQ Engine releases

Thanks to @MPConda for the idea and inspiration!