Add Streamable HTTP documentation

[omgitsads]

Summary

Adds documentation for new Streamable HTTP server mode.

Why

We need docs for it 😄

What changed

• Adds documentation to docs/ directory
• Adds reference to README.md (TODO)

MCP impact

• No tool or API changes
• Tool schema or behavior changed
• New tool added

Security / limits

• No security or limits impact
• Auth / permissions considered
• Data exposure, filtering, or token/size limits considered

Tool renaming

• I am renaming tools as part of this PR (e.g. a part of a consolidation effort)
  • I have added the new tool aliases in deprecated_tool_aliases.go
• I am not renaming tools as part of this PR

Note: if you're renaming tools, you must add the tool aliases. For more information on how to do so, please refer to the official docs.

Lint & tests

• Linted locally with ./script/lint
• Tested locally with ./script/test

Docs

• Not needed
• Updated (README / docs / examples)

[Copilot]

Pull request overview

Adds new documentation describing how to run and configure the GitHub MCP Server in Streamable HTTP (HTTP server) mode, including OAuth protected resource metadata and scope-challenge behavior.

Changes:

• Added docs/streamable-http.md with HTTP-mode overview, feature list, and CLI examples.
• Documented OAuth protected resource discovery and scope-challenge behavior.
• Added client configuration examples (URL + optional headers).

Comments suppressed due to low confidence (1)

docs/streamable-http.md:85

• Same issue as above: this example uses https://localhost:8082, but the built-in HTTP server does not serve TLS by default. Use http:// (or document that a TLS-terminating reverse proxy is required).

{
  "type": "http",
  "url": "https://localhost:8082",
  "headers": {