Perform multiple searches in one single HTTP request

[brunoocasali]

⚠️ This issue is generated, it means the examples and the namings do not necessarily correspond to the language of this repository.
Also, if you are a maintainer, feel free to add any clarification and instruction about this issue.

Sorry if this is already partially/completely implemented, feel free to let me know about the state of this issue in the repo.

Related to meilisearch/integration-guides#251

---

Related to:

• issue: Perform multiple searches in a single query meilisearch#3427
• spec: Multi Search API specifications#225

Create a new client method called multiSearch/multi_search, which will request POST /multi-search with a body payload containing a structure similar to this:

{
   "queries": [ 
      { "indexUid": "movie", "q": "wonder", "limit": 10 }, 
      { "indexUid": "books", "q": "king", "page": 2 } 
    ]
}

Each object is a simple search object sent in the POST /indexes/:indexUid/search request.

Pay attention to the response, which will follow the order of the requests object and will look like this (note the new indexUid key in the response):

{
   "results": [ 
      {
         "indexUid": "movie",
         "hits": [ { "title": "wonderwoman" } ],
         // other search results fields: processingTimeMs, limit, ...
      },
      {
         "indexUid": "books",
         "hits": [ { "title": "king kong theory" } ],
         // other search results fields: processingTimeMs, limit, ...
      },
   ]
}

TODO:

• Add the new multi_search method
• Add tests