Allow MPTT updates when uploading tree to ensure proper order.

[kollivier]

Description

Our ricecooker API for adding nodes uses disable_mptt_updates and defers tree processing until finalize_channel is called. However, after the removal of sort_order, this causes MPTT to order the nodes incorrectly. Correct this by removing the disable_mptt_updates call and allowing MPTT to order the tree properly at add time.

Currently this PR has only been manually tested. Ideally, we would have a unit test that confirms the order of children, but unit tests can confirm changes do not introduce regressions.

Note that we'll want to run this with a large-ish tree on hotfixes to ensure performance isn't impacted too significantly. (I can take care of this part.)

Steps to Test

• Run a large sushi chef

Checklist

• Is the code clean and well-commented?
• Are there tests for this change?

Reviewers

If you are looking to assign a reviewer, here are some options:

• Jordan jayoshih (full stack)
• Aron aronasorman (back end, devops)
• Micah micahscopes (full stack)
• Kevin kollivier (back end)
• Ivan ivanistheone (Ricecooker)
• Richard rtibbles (full stack, Kolibri)
• Radina @radinamatic (documentation)

[codecov]

Codecov Report

Merging #2954 (33434c2) into hotfixes (28587f8) will increase coverage by 4.77%.
The diff coverage is 93.00%.

@@             Coverage Diff              @@
##           hotfixes    #2954      +/-   ##
============================================
+ Coverage     80.80%   85.58%   +4.77%     
============================================
  Files           281      299      +18     
  Lines         12659    15885    +3226     
============================================
+ Hits          10229    13595    +3366     
+ Misses         2430     2290     -140     

Impacted Files	Coverage Δ
contentcuration/contentcuration/decorators.py	56.60% <50.00%> (-37.60%)	⬇️
...ntentcuration/contentcuration/db/models/manager.py	91.20% <90.98%> (-8.80%)	⬇️
contentcuration/contentcuration/forms.py	82.85% <94.31%> (+34.40%)	⬆️
contentcuration/contentcuration/api.py	92.06% <100.00%> (+1.43%)	⬆️
...tentcuration/contentcuration/context_processors.py	100.00% <100.00%> (ø)
...ontentcuration/contentcuration/db/advisory_lock.py	100.00% <100.00%> (ø)
...tcuration/contentcuration/db/models/expressions.py	93.33% <100.00%> (-6.67%)	⬇️
...entcuration/contentcuration/db/models/functions.py	100.00% <100.00%> (ø)
...ation/contentcuration/tests/test_rest_framework.py	36.93% <0.00%> (-63.07%)	⬇️
contentcuration/contentcuration/utils/format.py	21.05% <0.00%> (-49.54%)	⬇️
... and 181 more

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