Add integration test for DL2-to-DL3 step

[HealthyPear]

This PR adds the test for the last step of the pipeline.

I had to modify (actually slightly improve) the CLI of the script in order to overwrite some of the input settings coming from the configuration file.

I also added some development code from pyirf to allow the writing of empty tables of DL3 information in case no DL2 events are selected from the analysis (it happens with the prod3b CTAN test analysis).

The integration test checks that the script doesn't crash (for any reason) and that the output file has the expected number of HDUs from the current script and that each HDU has some data in it.

[codecov]

Codecov Report

Merging #137 (fc7212f) into master (e7825c0) will increase coverage by 5.24%.
The diff coverage is 89.36%.

@@            Coverage Diff             @@
##           master     #137      +/-   ##
==========================================
+ Coverage   60.35%   65.59%   +5.24%     
==========================================
  Files          23       23              
  Lines        2101     2142      +41     
==========================================
+ Hits         1268     1405     +137     
+ Misses        833      737      -96     

Impacted Files	Coverage Δ
protopipe/perf/__init__.py	100.00% <ø> (ø)
protopipe/scripts/make_performance_EventDisplay.py	95.32% <70.58%> (+73.54%)	⬆️
protopipe/perf/temp.py	100.00% <100.00%> (+76.47%)	⬆️
protopipe/perf/utils.py	57.57% <100.00%> (+33.04%)	⬆️
protopipe/scripts/tests/test_pipeline.py	100.00% <100.00%> (ø)
protopipe/pipeline/event_preparer.py	65.23% <0.00%> (-4.93%)	⬇️
... and 1 more

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