Add Sync Indexes API

[Sherlouk]

Pull Request

Related issue

Fixes #367

What does this PR do?

• Introduces new swapIndexes API. This is NOT a breaking change.
• Adds a new "wait" function to TaskInfo for cleaner async code (additive).

Worth noting that the above issue references an "API key action" and an error code. Neither of these are currently stored in the package and thus no changes needed.

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!

[curquiza]

Thank you @Sherlouk

LGTM 👌

bors merge

[meili-bors]

Build succeeded:

• integration-tests on macos-latest
• integration-tests on ubuntu-20.04
• linter-check