Get documents by filter

[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#261

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This issue is divided in two sections, first you need to make the implementation, second you must update the code-samples (no one likes a outdated docs, right?).

New implementation

Related to:

• issue: Delete and get documents by filter meilisearch#3477
• spec: Specify the new fetch documents route specifications#234

Gives the user the possibility to use a filter expression to retrieve documents, like in search.

Implement in the getDocuments method an internal conditional allowing the user to query the documents with the same method but using a new filter method.

When the user calls the get documents method with a filter argument, request POST /indexes/{index_uid}/documents/fetch using a JSON body containing an int offset, int limit, String[] fields and now String filter or String[] filter.
⚠️ If the method invocation does not contain a filter it should still call the previous implementation.

Code samples:

Inside of this file: .code-samples.meilisearch.yml:

1. Replace this key: get_documents_1: content to use the filter genres=action, keep the index name and the limit just add the filter.
   Use this as a reference if the previous description was not helpful::

get_documents_1: |- 
  GET 'http://localhost:7700/indexes/movies/documents?limit=2&filter=genres=action
  mind the filter in the query param (use the POST route in the integrations)

2. Create a new entry with this key get_documents_post_1: containing a call to the getDocuments method
   using the new behavior from the index movies using the filter param with this string "genres = action OR genres = adventure".

Use this as a reference if the previous description was not helpful:

get_documents_post_1: |-
  POST http://localhost:7700/indexes/books/documents/fetch
  with data: { 
    "filter": "(rating > 3 AND (genres = Adventure OR genres = Fiction)) AND language = English",
    "fields": ["title", "genres", "rating", "language"],
    "limit": 3
  }

Todo:

• Implement the getDocuments new behavior keeping the old behavior when possible.
• Update the code-samples according to this issue.