Add Federation Parameter to multisearch method

[Nsreddy18]

Pull Request

Related issue

Fixes #768

What does this PR do?

• Adds a new parameter federation to the multiSearch method.
• Introduces a new search parameter federationOptions to the search query.
• Adds a getter method to the MultiSearchRequest class to retrieve the query list for creating the payload.
• Adds a test to validate the new functionality.

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 youuuu

bors merge

[meili-bors]

Build succeeded:

• integration-and-unit-tests
• linter