feat: Enable metadata length field config by environment variable

[frascuchon]

Closes #1761

[codecov]

Codecov Report

Base: 94.59% // Head: 94.59% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (8a60223) compared to base (8aec980).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1923   +/-   ##
========================================
  Coverage    94.59%   94.59%           
========================================
  Files          149      150    +1     
  Lines         7025     7036   +11     
========================================
+ Hits          6645     6656   +11     
  Misses         380      380           

Flag	Coverage Δ
pytest	94.59% <100.00%> (+<0.01%)	⬆️

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

Impacted Files	Coverage Δ
src/argilla/server/daos/backend/elasticsearch.py	86.03% <ø> (ø)
src/argilla/_constants.py	100.00% <100.00%> (ø)
src/argilla/_messages.py	100.00% <100.00%> (ø)
src/argilla/client/models.py	94.14% <100.00%> (+0.22%)	⬆️
.../argilla/client/sdk/token_classification/models.py	100.00% <100.00%> (ø)
...rc/argilla/server/daos/backend/mappings/helpers.py	98.46% <100.00%> (-0.03%)	⬇️
src/argilla/server/daos/models/records.py	97.16% <100.00%> (+0.14%)	⬆️
...server/services/tasks/text_classification/model.py	99.32% <100.00%> (ø)
...erver/services/tasks/token_classification/model.py	98.97% <100.00%> (-0.04%)	⬇️
src/argilla/server/settings.py	76.66% <100.00%> (+0.80%)	⬆️

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