WIP refactor(backend): reduce surface by unifying metadata endpoints

[matmair]

Replaces individual metadata endpoints with a generic endpoint and a bunch of permanent redirects. Obviously a breaking change.
This:

• reduces the amount of duplicated endpoints doing the same things and the required tests too
• removes the necessity to declare new endpoints for every metadata-supporting model
• is plugin friendly as models defined in those can also use the new endpoint

[netlify]

✅ Deploy Preview for inventree-web-pui-preview canceled.

Name	Link
🔨 Latest commit	c76f4f5
🔍 Latest deploy log	https://app.netlify.com/projects/inventree-web-pui-preview/deploys/6948fc3feb11c0000849b4a5

[codecov]

Codecov Report

❌ Patch coverage is 88.60759% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.16%. Comparing base (947a3e2) to head (c76f4f5).

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #11035      +/-   ##
==========================================
- Coverage   88.18%   88.16%   -0.03%     
==========================================
  Files        1290     1290              
  Lines       58112    58115       +3     
  Branches     1969     1969              
==========================================
- Hits        51244    51235       -9     
- Misses       6377     6389      +12     
  Partials      491      491              

Flag	Coverage Δ
backend	89.45% <88.60%> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
Backend Apps	92.01% <100.00%> (-0.02%)	⬇️
Backend General	93.48% <100.00%> (ø)
Frontend	70.86% <ø> (ø)

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