[v1.9.0] Get similar documents

[Clémentine]

Related to meilisearch/integration-guides#301

Explanation of the feature

Introduction of a new route to get similar documents

Usage: https://meilisearch.notion.site/Get-similar-documents-usage-540919ca755c4da0b7cdee273db3f290?pvs=74

TODO

• Add a new method named searchSimilarDocuments() having 1 parameter. This parameter is an object correspond to the body you should pass to the POST /similar route. Do not manage error, Meilisearch will handle them if a field is missing in the body.
  Do NOT implement the route for GET /similar, we will add it in a second iteration if requested.
• Add tests. Here is the basic test to do to check everything is fine

⚠️ Make PRs pointing to bump-meilisearch-v1.9.0 and NOT main. Please do 1 PR for all of these changes, and not several.

[Clémentine]

Closed by #1677