Fix using distinct attribute setting

[norkunas]

Pull Request

Related issue

Fixes #273

What does this PR do?

• Fixes updating distinct attribute setting and allows to set it as a string instead of an array

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• Does this PR fix an existing issue, or have you listed the changes applied in the PR description (and why they are needed)?
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Temporary fix until we'll provide proper configuration schema for each setting separately.

[brunoocasali]

Nice to keep the backwards compatibility (even if that didn't work 😅)

Thanks @norkunas 🎉

bors merge

[meili-bors]

Build succeeded:

• Code style
• integration-tests (PHP 7.4) (Symfony 5.4.*)
• integration-tests (PHP 8.0) (Symfony 6.0.*)
• integration-tests (PHP 8.1) (Symfony 6.1.*)
• integration-tests (PHP 8.2) (Symfony 6.2.*)
• integration-tests (PHP 8.3) (Symfony 6.3.*)