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
- [ ] /document/{identifier}
- [ ] https://github.com/openfoodfacts/openfoodfacts-dart/issues/841
- [ ] /autocomplete

### Schemas
- [ ] ErrorSearchResponseExpand allobject
- [ ] HTTPValidationErrorExpand allobject
- [ ] SearchResponseDebugExpand allobject
- [ ] SearchResponseErrorExpand allobject
- [ ] SuccessSearchResponseExpand allobject
- [ ] ValidationErrorExpand allobject

### Sub-issues already opened
- [ ] #620 
- [ ] #619 

Related issue in the official mobile app

• https://github.com/openfoodfacts/smooth-app/issues/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.