Implement the new ElasticSearch search endpoint

[teolemon]

Why - Problem description

• As part of the search revamp project, we will be deploying a new Elasticsearch endpoint at https://search.openfoodfacts.org/docs#/
• It will be OpenAPI compatible so we can generate a base Flutter SDK automatically that we can draw from here.
• We will also be upgrading the classic product-opener search to use this backend in the background (with an unchanged API vs what we've already implemented), so we should not deprecate immediately classic search.
• We should also implement direct calls to the Elasticsearch endpoint. This will pave the way for a fuller search implementation in Smoothie.

URL of the doc

https://search.openfoodfacts.org/docs#/

Routes

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1. /document/{identifier}
2. /search #841
   🎯 P0 🔎 Search +2
3. /autocomplete

Schemas

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1. ErrorSearchResponseExpand allobject
2. HTTPValidationErrorExpand allobject
3. SearchResponseDebugExpand allobject
4. SearchResponseErrorExpand allobject
5. SuccessSearchResponseExpand allobject
6. ValidationErrorExpand allobject

Sub-issues already opened

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1. Use the new ElasticSearch endpoint to provide search as you type product suggestions #620
   🎯 P0 🔎 Search +2
   
2. Use the new ElasticSearch endpoint to provide as you type brand suggestions #619
   autocomplete brands requires server change 🎯 P1 +4
   

Related issue in the official mobile app

• 🔍 Search (tracker) smooth-app#991

[monsieurtanuki]

My first tests show some problems/questions.

parameter discrepancies

In the current version

1. we pass the country as a parameter
   => shouldn't we do so Elastic Search?
2. we pass app_name as a parameter
   => shouldn't we do so Elastic Search?
3. we pass the user name in the http header
   => shouldn't we do so Elastic Search?

product structure discrepancies

In the current version
4. the "brands" product field is a comma-separated String, and in Elastic Search it's a List<String>.
=> it probably means that we need a specific new Product class.