feat: add pluggable override for learner home enterprise customer lookup

[pwnage101]

ENT-11571

Migrates functionality from openedx-platform to look up a user's enterprise status and populate
enterpriseDashboard in /api/learner_home/init/ endpoint.

---

Related:

• feat: replace enterprise imports in learner_home/views.py with pluggable_override edx/edx-platform#383
• feat: add pluggable override for learner home enterprise customer lookup #2554
• feat: replace enterprise imports in learner_home/views.py with pluggable_override openedx-platform#38107

[pwnage101]

Clarify comment that this defensive import is only here temporarily because the plan is ultimately to migrate the entire enterprise_support app into edx-enterprise.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.70%. Comparing base (681a2c7) to head (e2a1c64).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2554      +/-   ##
==========================================
+ Coverage   86.68%   86.70%   +0.01%     
==========================================
  Files         258      259       +1     
  Lines       16995    17016      +21     
  Branches     1680     1681       +1     
==========================================
+ Hits        14732    14753      +21     
  Misses       1927     1927              
  Partials      336      336              

Flag	Coverage Δ
unittests	86.70% <100.00%> (+0.01%)	⬆️

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[pwnage101]

✅ LGTM!