Feat support text-separator customization

[Ja7ad]

Pull Request

Related issue

Fixes #488

What does this PR do?

• Support text-separator customization

PR checklist

Please check if your PR fulfills the following requirements:

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

Thank you so much for contributing to Meilisearch!

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 86.04651% with 12 lines in your changes missing coverage. Please review.

Project coverage is 86.76%. Comparing base (ad4b0b2) to head (b6f48e5). Report is 6 commits behind head on main.

Files	Patch %	Lines
index_settings.go	86.04%	6 Missing and 6 partials :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #559 +/- ## ========================================== - Coverage 86.79% 86.76% -0.04% ========================================== Files 11 11 Lines 1856 1957 +101 ========================================== + Hits 1611 1698 +87 - Misses 152 159 +7 - Partials 93 100 +7 ```

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[meili-bors[bot]]

Build succeeded:

• integration-tests (go current version)
• integration-tests (go latest version)
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