[v1.3] Define fields to search on at search-time (`attributesToSearchOn`)

[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, please add any clarification and instructions about this issue.

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

Related to meilisearch/integration-guides#280

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New implementation

Related to:

• issue: Define field to search on at search-time meilisearch/meilisearch#3772
• discussion: Define field to search on at search-time meilisearch/product#107 (comment)
• spec: Define fields to search on at runtime  meilisearch/specifications#251

Add support for receiving a new key, attributesToSearchOn (an array of field names), to enable running searches over a subset of searchableAttributes without modifying Meilisearch’s index settings.

TODO:

• Add the ability to receive a new param in the search method called attributesToSearchOn.
• Add integration tests