v1.8: Generic REST embedder

[gui machiavelli]

v1.8 introduces a generic embedder option compatible with any embedders offering a RESTful interface.

Tasks

• Add new section to Vector search page

References

• engine issue: meilisearch/meilisearch#4531
• PRD: https://meilisearch.notion.site/v1-8-AI-search-API-usage-135552d6e85a4a52bc7109be82aeca42#e6f58c3b742c4effb4ddc625ce12ee16
• SME: @dureuill