Allow config files to be from a remote repository

[sampart]

You can see an example of this in use in a branch that builds off this one. Here's a deep link to the Actions run, showing the HTTP request: https://github.com/github/codeql-action/runs/811641896?check_suite_focus=true#step:4:27

[robertbrignull]

The code LGTM and the test that you included looks good too.

Only thing I can think of to improve it would be to add an entry to https://github.com/github/codeql-action/blob/main/.github/workflows/integration-testing.yml so it gets tested automatically as well.

[sampart]

Thanks @robertbrignull. I've had a go at adding an integration test in 4b37db7; I'd appreciate your eyes on that one, thanks! In particular, can we simplify the checkout?

[robertbrignull]

I'd copy what the existing integration tests do, instead of using the format from the public template. There's no need to do the fetch-depth and custom checkout step for the integration tests. I'd just copy multi-language-repo_test-custom-queries but change the reference to the config file to be a remote repository reference.

[robertbrignull]

Or you could even change that existing test so it tests both aspects at once. We don't have a good guideline for this. I'm wary of introducing too many extra tests, especially if they all test on multiple OS's, because the tests will start taking up too many action minutes and take too long. It's unclear if we've reached that point or not yet. And since we can always change the test setup at any point, whatever you do we can always adjust in the future.

[sampart]

Sounds like a plan, thanks. Done in 1bb294a.

[robertbrignull]

Thanks for adding the integration test. LGTM