Remove default order for searchableAttributes following v1.9.0

[dureuill]

Hello 👋

As of v1.9.0, all fields now have the same impact on relevancy when searchableAttributes: ["*"].

This change is detailed in meilisearch/meilisearch#4639 and was implemented in the docs in #2852

However, it looks like the phrasing "all attributes are automatically added to the searchableAttributes list in their order of appearance" remains ambiguous: see issue here and should probably be updated to specify that all fields will then have the same weight.