[Meilisearch v1.48.0] Add document relations (experimental)

Context

Meilisearch introduced document relations as an experimental feature.

Objective

Add support for the document relations settings as an experimental feature. Experimental features should require opt-in by the user. Read the how to guide for more information.

Tasks

• Add methods to interact with Get foreignKeys, Update foreignKeys, and Reset foreignKeys API endpoints
• Update the global settings methods to accept and handle the foreignKeys setting
• Add test cases for all new methods
• Add code samples in .code-samples.meilisearch.yaml matching the Meilisearch documentation CURL examples:
  • Under get_foreign_keys_setting_1: equivalent of this code sample
  • Under update_foreign_keys_setting_1: equivalent of this code sample
  • Under reset_foreign_keys_setting_1: equivalent of this code sample

Resources

Release notes:

• Meilisearch v1.39 introduced cross-index document hydration via a new foreignKeys index setting. This allows linking documents across indexes so that search results are automatically enriched with related data.
• Meilisearch v1.42 extended it with document join filtering — the ability to filter search results using the _foreign() filter syntax on related indexes. This requires the foreign key field to also be configured in filterableAttributes.
• Meilisearch v1.48 refined it by restricting foreign filters to retrieval routes only.

Start with the existing settings methods and their tests, then compare the foreignKeys API endpoints and the linked Meilisearch documentation. Add the three foreignKeys operations, support the setting in global settings, and cover each method with tests. Update .code-samples.meilisearch.yaml under get_foreign_keys_setting_1, update_foreign_keys_setting_1, and reset_foreign_keys_setting_1 to match the documented CURL examples.