APEx reference check needs better representation (ascii art diff, diff image, statistics)

[dsamaey]

Statistics are most important
#percentage of pixels that are different (tolerance)
median, mean, min, max
Perhaps write diff to a png -- Issue with dimensionality (per timestamp, per band) max 10 files.

Location of differences
Which timestamp(s) failed
Which band(s) failed
bbox of differences as geojson (so you can crop)

• it happens that changes are very concentrated

Extras
Numpy has something similar. We have unit tests that already print more informative messages.

Pipeline for cdse staging might not be configured yet for writing to s3 bucket. Ask @JeroenVerstraelen.

[soxofaan]

FYI:

initial comparison/assert utilities are defined in python client: https://github.com/Open-EO/openeo-python-client/blob/master/openeo/testing/results.py

test coverage of that (to give an idea about behavior): https://github.com/Open-EO/openeo-python-client/blob/master/tests/testing/test_results.py

Usage in APEx benchmark test suite is basically just this: https://github.com/ESA-APEx/apex_algorithms/blob/91eb3e62cc9e6d179b655baa97132771b5b0c6e8/qa/benchmarks/tests/test_benchmarks.py#L74-L80