chore: remove the rig example

[jokemanfire]

The rig official has the mcp example, we need not to keep it just give the link.

Motivation and Context

Reduce example maintenance work

How Has This Been Tested?

Breaking Changes

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[Copilot]

Pull request overview

This PR removes the in-repo rig-integration example to reduce maintenance burden, and replaces its listing in the examples index with a link to the upstream Rig MCP example.

Changes:

• Deleted the examples/rig-integration example crate (source, config, and manifest).
• Updated examples/README.md to point the Rig integration example to the upstream Rig repository.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
examples/rig-integration/src/mcp_adaptor.rs	Removed Rig↔MCP adaptor implementation as part of deleting the example.
examples/rig-integration/src/main.rs	Removed the example CLI entrypoint.
examples/rig-integration/src/config/mcp.rs	Removed MCP transport/server config for the example.
examples/rig-integration/src/config.rs	Removed example configuration loader/types.
examples/rig-integration/src/chat.rs	Removed streaming CLI chat UI for the example.
examples/rig-integration/config.toml	Removed example runtime configuration.
examples/rig-integration/Cargo.toml	Removed the example crate manifest from the workspace glob.
examples/README.md	Replaced local Rig example link with an external upstream link.

[DaleSeo]

Thanks for cleaning this up, @jokemanfire!