Distinct search parameter support added

[Barabasbalazs]

Pull Request

Related issue

Fixes https://github.com/meilisearch/meilisearch-java/issues/756

What does this PR do?

• Added support for using the distinct keyword in the java client. Updated tests and code samples accordingly.

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?

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