Ignore dependencies on Wikimedia config repositories

[MatmaRex]

Sometimes folks point 'Depends-On' entries to Wikimedia config repositories. We don't support them, but these dependencies are usually not needed to test a patch on Patch demo, so ignore them instead of erroring out.

Closes #573

[MatmaRex]

(I deployed this on https://patchdemo.wmflabs.org/ for testing, cc @MusikAnimal)

[MusikAnimal]

(I deployed this on https://patchdemo.wmflabs.org/ for testing, cc @MusikAnimal)

It worked great as far as building the wiki, but it appears composer install wasn't ran? I'm getting Exception caught: Class 'Endroid\QrCode\Builder\Builder' not found

I thought a908a611c0e881c8c45f88b21116ddd617d1aa8c was supposed to make that work. Or perhaps I'm missing something else?

[MatmaRex]

Ugh, it looks like we do the installation steps in the wrong order, running composer install before applying the patches. :/

[edg2s]

Could we instead just ignore anything that isn't in all.txt? If the repo isn't there we never pull in the Depends-On. We could show a warning in the log that not all dependencies were checked out, in case it's a dependency that should be pulled it, but just hasn't been added to Patch Demo yet.

[MatmaRex]

Yeah, that's a good idea, I think we could. I've been thinking in terms of "real" dependencies, where the other thing is needed to run the current thing, but that's now how we use Depends-On – it just indicates that the other patch needs to be merged before the current patch for smooth deployment in Wikimedia production, and "real" dependencies between extensions are indicated in extension.json, so failing to satisfy them will display a reasonable error anyway (but later in the process).

[MatmaRex]

See #577 instead