Replace children_count with has_children

Backend part of #473 (closed)

Benchmarks, listing top_level elements on Himanis:

Server	Nothing	children_count	has_children
manage.py runserver	315 ms	1392ms	762ms
Docker binary	161 ms	1195ms	550ms

Codecov Report

Merging #1020 into master will decrease coverage by 0.14%. The diff coverage is 65.78%.

@@            Coverage Diff             @@
##           master    #1020      +/-   ##
==========================================
- Coverage   88.11%   87.96%   -0.15%     
==========================================
  Files         230      231       +1     
  Lines       15225    15253      +28     
==========================================
+ Hits        13415    13418       +3     
- Misses       1810     1835      +25     

Impacted Files	Coverage Δ
arkindex/documents/management/commands/delete.py	0.00% <0.00%> (ø)
arkindex/documents/signals.py	73.33% <80.76%> (+13.33%)
arkindex/documents/api/elements.py	98.70% <92.30%> (-0.27%)
arkindex/documents/serializers/elements.py	98.56% <100.00%> (ø)
arkindex/documents/tests/test_children_elements.py	100.00% <100.00%> (ø)
arkindex/documents/tests/test_datasource.py	100.00% <100.00%> (ø)
arkindex/documents/tests/test_edit_elementpath.py	100.00% <100.00%> (ø)
arkindex/documents/tests/test_list_elements.py	100.00% <100.00%> (ø)
arkindex/documents/tests/test_parents_elements.py	100.00% <100.00%> (ø)
arkindex/documents/tests/test_retrieve_elements.py	100.00% <100.00%> (ø)
... and 1 more

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changed the description

assigned to @babadie and unassigned @erwanrouchet

added 1 commit

• e99ad624 - Ignore empty results

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mentioned in merge request frontend!721 (merged)

added 4 commits

• e99ad624...eb15470d - 2 commits from branch master
• 2ff00e23 - Replace children_count with has_children
• bab8d69b - Ignore empty results

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added 4 commits

• bab8d69b...bcb65c51 - 2 commits from branch master
• 938fd7cf - Replace children_count with has_children
• a12cbc34 - Ignore empty results

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added 16 commits

• a12cbc34...cb83de03 - 14 commits from branch master
• 83a78481 - Replace children_count with has_children
• 24fb9441 - Ignore empty results

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enabled an automatic merge when the pipeline for 24fb9441 succeeds

aborted the automatic merge because target branch was updated

added 4 commits

• 24fb9441...b5f6ca89 - 2 commits from branch master
• d6f578d3 - Replace children_count with has_children
• 8bb13470 - Ignore empty results

Compare with previous version

enabled an automatic merge when the pipeline for 8bb13470 succeeds

canceled the automatic merge

merged

mentioned in commit 1ad14f6b