[Search] Add api.md and api.metadata.yml for azure-search-documents

[hizixin]

Description

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• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
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Testing Guidelines

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[Copilot]

Pull request overview

This PR adds the generated API surface snapshot files for the azure-search-documents package: api.md (the textual API stub) and api.metadata.yml (metadata used by the API-md consistency CI check). These files allow CI to detect unintended API surface changes by comparing committed snapshots against freshly generated ones.

Changes:

• Adds api.metadata.yml with apiMdSha256, parserVersion (0.3.28), and pythonVersion (3.12.13).
• Adds the corresponding api.md capturing the public API surface of azure.search.documents.

Reviewed changes

Copilot reviewed 1 out of 2 changed files in this pull request and generated no comments.

File	Description
sdk/search/azure-search-documents/api.metadata.yml	Adds API metadata (hash + parser/python versions) consumed by the api-md consistency CI gate; follows the standard 3-key format.
sdk/search/azure-search-documents/api.md	Adds the generated API surface snapshot (not shown in the visible diff); verified present and well-formed.