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two sections, first, you need to make the implementation, and second, you must update the code-samples (no one likes outdated docs, right?).

New implementation

Related to:

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

Code samples

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

1. Create a new entry with this key search_parameter_guide_attributes_to_search_on_1 containing a call to the search method using the new behavior.
   Refer to this curl example, and "translate" it by using go methods: https://github.com/meilisearch/documentation/blob/e4fdc3d485c22e31a045b8a71bacf18b6a7d50e0/.code-samples.meilisearch.yaml#L1103

TODO:

• Add the ability to receive a new param in the search method called attributesToSearchOn.
• Add integration tests
• Update the code-samples accordingly

[curquiza]

Closed by #458
and #493