Automatically test examples for new PRs

[RuaridhMacd]

@Betristor

• Create a workflow in GitHub Actions to test the three SmallNewEngland cases using HiGHs after each PR
• Base off of genx_as_submodule
• Use Documentation.yml as a template

[Betristor]

@RuaridhMacd I write a runtest.jl using Test pkg to automatically run test scripts for us. But i can only manage to have it work locally after you activate local environment and type test in pkg management mode. To have this test work on github actions, I believe I need to figure out how to install highs solver on the machine that github will use when the action is triggered.
BTW, I checked GenX's runtests script, they just used some simple operations like addition which is invalid in testing. You could find new changes made to your branch on testDolphyn branch.
Anna's ThreeZones_Liquid case still fails in my situation. So I commented test script for her case. If it's functionable, test could be added at any time.
Sorry that I decided not to use Documentation.yml as example, I've found a test script dedicated for julia test called Run Julia package test created by julia-actions. The next step is to figure out how to install highs solver on the test environment.

[RuaridhMacd]

• @RuaridhMacd Take a look at the Gtihub Actions log files to diagnose error
• @Betristor Work out how to download and install HiGHs to a Github Actions machine
• @Betristor Ask Greg Schivley on the Princeton about installing HiGHs

[Betristor]

@RuaridhMacd I believed that PR #156 has fulfilled things we required here. And I found that highs binary is not needed to perform the tests, at least in ubuntu machines. I'd like to close this issue with PR #156 merged.

[RuaridhMacd]

Resolved by #173