docs: add supported headers reference documentation

[Radheshg04]

s## Add comprehensive HTTP headers documentation

This PR adds a new documentation page that provides a complete reference of all HTTP headers supported by Bifrost gateway. The documentation includes context keys, types, descriptions, and usage examples for each header.

Changes

• Added new documentation page docs/providers/supported-headers.mdx with comprehensive header reference
• Updated navigation in docs/docs.json to include the new page
• Enhanced existing documentation in provider configuration and context keys pages to reference the new headers documentation
• Added documentation for the passthrough extra parameters feature (x-bf-passthrough-extra-params header)

Type of change

• Bug fix
• Feature
• Refactor
• Documentation
• Chore/CI

Affected areas

• Core (Go)
• Transports (HTTP)
• Providers/Integrations
• Plugins
• UI (Next.js)
• Docs

How to test

The documentation can be tested by running the docs site locally:

cd docs
npm install
npm run dev

Then navigate to the new page at /providers/supported-headers to verify the content.

Breaking changes

• No

Related issues

Addresses the need for comprehensive header documentation to help users understand all available request configuration options.

Checklist

• I read docs/contributing/README.md and followed the guidelines
• I updated documentation where needed
• I verified builds succeed (Go and UI)

[coderabbitai]

📝 Walkthrough

Summary by CodeRabbit

• Documentation
  • Added comprehensive reference documentation for request options and configuration parameters
  • Documented passthrough extra parameters feature for both gateway and Go SDK implementations
  • Added new documentation page for request options reference
  • Updated URL redirect for improved navigation

_{✏️ Tip: You can customize this high-level summary in your review settings.}

Walkthrough

This PR adds documentation for a new "Passthrough Extra Parameters" feature that allows parameters in extra_params to bypass Bifrost's parameter filtering. It introduces a comprehensive request options reference page, updates navigation and redirects, documents the feature across gateway and Go SDK examples, and exports a new context key constant.

Changes

Cohort / File(s)	Summary
Navigation & Redirects docs/docs.json	Inserted new nav page providers/request-options under "Supported Providers" and added redirect from /providers/supported-headers to /providers/request-options.
Gateway Docs docs/quickstart/gateway/provider-configuration.mdx	Added "Passthrough Extra Parameters" sections with description, behavior notes (JSON-only, recursive merge, no duplication), and curl example.
Go SDK Docs & API Surface docs/quickstart/go-sdk/context-keys.mdx	Documented passthrough usage, added examples, and introduced exported constant BifrostContextKeyPassthroughExtraParams in schemas.
Request Options Reference docs/providers/request-options.mdx	New comprehensive reference documenting gateway headers, Go SDK context keys, request options, caching, observability, security denylist, examples, and forwarding behavior.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~12 minutes

Poem

🐇 I hopped through docs with a curious cheer,
Extra params whispered, "Let us steer,"
Passthrough opened a path, tidy and bright,
Gateway, SDK—now all sing in light,
Hooray, says the rabbit, for clearer request flight!

🚥 Pre-merge checks | ✅ 3

✅ Passed checks (3 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately describes the main change: adding documentation for supported headers. It is concise, clear, and directly reflects the primary objective of the PR.
Description check	✅ Passed	The description comprehensively covers the PR purpose, lists all changes made, identifies it as a documentation change, specifies affected areas (Docs), includes testing instructions, confirms no breaking changes, and includes most checklist items completed.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment
• Commit unit tests in branch 01-30-feat_added_supported_headers_page_and_updated_docs

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[Radheshg04]

• docs: add supported headers reference documentation #1488 👈 (View in Graphite)
• fix: ensure ExtraParams are propagated into provider request body #1485
• main

This stack of pull requests is managed by Graphite. Learn more about stacking.

[akshaydeo]

Merge activity

• Jan 30, 6:28 PM UTC: A user started a stack merge that includes this pull request via Graphite.
• Jan 30, 6:29 PM UTC: @akshaydeo merged this pull request with Graphite.