Move generate_ground_truth_recording to generation module

[h-mayorquin]

This was left out by mistake from #4520. generate_ground_truth_recording should also be in the generation module to avoid a dependency of core into generation.

I also dropped strategy= from test fixtures and the two production callsites that pass it explicitly, keeping the kwarg itself defined on the NoiseGeneratorRecording and MockRecording classes (whose removal is under discussion in #4522). This overlaps with the callsite cleanup in @cwindolf's #4586 (temporally-correlated noise V2, which follows on from #4587) and should make that PR cleaner. Both branches edit the same lines, so the merge should resolve cleanly regardless of order.

[samuelgarcia]

Even it looks noisy, I was happy with the explicit strategy= everywhere.
In my mind, it was :

• generate me a fast random noise, I don't care
• or generate me a better noise even if it is slower

And more importantly we absolutly need that this must use always 'on_the_fly' !!!

[h-mayorquin]

Even it looks noisy, I was happy with the explicit strategy= everywhere. In my mind, it was :

• generate me a fast random noise, I don't care
• or generate me a better noise even if it is slower

And more importantly we absolutly need that this must use always 'on_the_fly' !!!

I agree with the on_the_fly. The other strategy does not make sense for the scope of the generate_ground_truth os I don't think it should be there.