OpenAPI — Verify and fix Content-Type header description

[gmourier]

The header content-type seems to have been introduced in places where it isn't required in the open-api spec. Moreover, we don't describe the other accepted content types (ndjson, csv) for the document addition/update routes.

[gmourier]

v1.2 and v1.3 open-API changelog mention a breaking change while it's not true. Wondering if that openAPI warning will solve that situation if managed. (it's a common warning for both versions)

https://bump.sh/meilisearch/docs/0772e3a7-2923-4d62-95e3-c4339c525968/versions?filter%5Bstatus%5D=released

We have detected some duplicate 'operationId' attributes on 2 different operations within your file. Please make sure the following operations have a unique identifier: "POST /indexes/{indexUid}/documents/delete", "DELETE /indexes/{indexUid}/documents/{documentId}".