Semantic search refactor: split haml file into partials

What does this MR do and why?

This splits the ee/app/views/admin/application_settings/semantic_search_embeddings/show.html.haml into partials according to sections:

• the read-only display section
• the embedding model inputs section (with a heading added)
• the chunking strategy inputs section

This is in preparation for supporting embeddings_request_batch_size updates from the Admin UI. The full change can be seen in the PoC MR Allow SM Admins to update embeddings request ba... (!246635 - merged), which needed to be split up due to its size.

Change steps

• Introduce the embeddings_request_batch_size as a collection option - !246085 (merged)
• Refactor: update the "Semantic search embeddings UI" to split haml into partials - This MR
• Allow administrators to update the indexing batch size through the Admin UI - TBA, see PoC MR

References

• Issue: [Semantic Search] Persist batch_size for indexing (#600634 - closed)
• POC MR: Allow SM Admins to update embeddings request ba... (!246635 - merged)

Screenshots or screen recordings

Embedding model not yet configured	Embedding model configured

How to set up and validate locally

This is a basic refactor to split a haml file into partials, the screenshots above should be enough.

The controller spec (ee/spec/requests/admin/application_settings/semantic_search_embeddings_controller_spec.rb), which hasn't changed, should also be enough for testing.

MR acceptance checklist

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Related to #600634 (closed)