Add posibility to use an existing persistence claim

[nlamirault]

Pull Request

Related issue

Fixes #82

What does this PR do?

• ...

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!

[alallema]

bors merge

[bors[bot]]

Build succeeded:

• check-chart-manifest-in-sync
• helm-tests
• linter