Deprecate output_format='dict'

[PGijsbers]

Deprecates output_format='dict':

• add a future warning with any of the list_* functions are called with output_format='dict',
• update all internal code and examples which used to rely on the default of output_format='dict'

WIP: Going through unit tests I incidentally broke

[LennartPurucker]

Looks good to me at this point.

[codecov-commenter]

Codecov Report

Patch coverage: 86.20% and project coverage change: +3.84 🎉

Comparison is base (3b3553b) 81.66% compared to head (c130c41) 85.51%.

❗ Current head c130c41 differs from pull request most recent head 22a6dd3. Consider uploading reports for the commit 22a6dd3 to get more accurate results

Additional details and impacted files

@@ Coverage Diff @@## develop #1258 +/- ##
===========================================
+ Coverage 81.66% 85.51% +3.84% 
===========================================
Files 38 38 Lines 5012 5343 +331 ===========================================
+ Hits 4093 4569 +476 + Misses 919 774 -145 

Impacted Files	Coverage Δ
openml/study/functions.py	85.36% <25.00%> (-5.19%)	⬇️
openml/evaluations/functions.py	82.35% <50.00%> (+11.04%)	⬆️
openml/flows/functions.py	83.97% <50.00%> (-0.77%)	⬇️
openml/tasks/functions.py	84.73% <75.00%> (+1.04%)	⬆️
openml/datasets/dataset.py	87.55% <91.07%> (+1.77%)	⬆️
openml/datasets/functions.py	93.01% <93.93%> (+4.76%)	⬆️
openml/datasets/data_feature.py	71.42% <100.00%> (+2.19%)	⬆️
openml/runs/functions.py	84.13% <100.00%> (+8.71%)	⬆️
openml/setups/functions.py	93.08% <100.00%> (+7.14%)	⬆️
openml/utils.py	92.21% <100.00%> (+0.34%)	⬆️

... and 9 files with indirect coverage changes

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[PGijsbers]

I think I cleared up the tests I accidentally broke after refactoring, but there are a lot of failures due to the test server state (also on develop). I would prefer to wait until we have working CI again.

[PGijsbers]

@mfeurer only test_list_all_with_multiple_batches fails now, as expected. I think we can go ahead and merge this.