[CN] Add CI for CN runtime testing capability

[septract]

Runs the CN runtime testing capability over specially-modified examples from the CN tutorial.

Note:

• The CI script checks out branch CN-exec: Upgrade single file runtime test script #439, which includes necessary test script modifications. Before merging this branch, we need to merge CN-exec: Upgrade single file runtime test script #439 and then the checkout target should be changed to cerberus:master
• The CI script applies the runtime testing to cn-tutorial:cn-runtime-testing. This branch adds main() functions to the tutorial examples, and so it cannot be merged into cn-tutorial:main. It's okay to merge without resolving this, but we should fix it sooner rather than later.

[septract]

@rbanerjee20

[rbanerjee20]

I've approved #439 now so once that is merged I'm happy to approve and merge this PR too.

[septract]

@rbanerjee20 Looks like this is working! If you're happy with the PR, go ahead and merge.

[septract]

Note this PR still points to a branch on cn-tutorial - see here: rems-project/cn-tutorial#70

Okay to merge as is, but we should fix this at some point soon.

@dc-mak

[dc-mak]

Just for posterity, 8722102 has the wrong issue number, it should be #489 but I got it wrong in a rush.