Add sort_facet_values_by to Faceting model

[sanders41]

Pull Request

@curquiza this is what is needed in addition to the code samples for #829

Related issue

Fixes #829

What does this PR do?

• Adds sort_facet_values_by to the Faceting model

PR checklist

Please check if your PR fulfills the following requirements:

• Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
• Have you read the contributing guidelines?
• Have you made sure that the title is accurate and descriptive of the changes?

Thank you so much for contributing to Meilisearch!

[codecov]

Codecov Report

Patch coverage: 100.00% and no project coverage change.

Comparison is base (a4b6513) 100.00% compared to head (715a9e9) 100.00%.
Report is 6 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #848   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           13        13           
  Lines          720       721    +1     
=========================================
+ Hits           720       721    +1     

Files Changed	Coverage Δ
meilisearch/models/index.py	100.00% <100.00%> (ø)

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[curquiza]

Thank you @sanders41

I let you merge when you want 😄

[sanders41]

bors merge

[meili-bors]

Build succeeded:

• integration-tests (3.10)
• integration-tests (3.11)
• integration-tests (3.8)
• integration-tests (3.9)
• mypy
• pylint