[v1.9] Get similar documents

[Clémentine]

Following this central issue

This is related to a newly introduced feature in Meilisearch v1.9.0: get similar documents.

Refer to docs for more information.

• Add a new method named searchSimilarDocuments() (adapt the case to the language) having 1 parameter. This parameter is an object corresponding 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 /indexes/{index_uid}/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
• Update the .code-samples.meilisearch.yaml
  • Add get_similar_post_1 key and “translate” the following curl example by using the newly added methods: https://github.com/meilisearch/documentation/blob/04f26a35771305378ed0a506f4d60ef06d07bd7e/.code-samples.meilisearch.yaml#L1333-L1340