feat: add a new mcp call

[cdavernas]

Please specify parts of this PR update:

• Specification
• Schema
• Examples
• Extensions
• Use Cases
• Community
• CTK
• Other

Discussion or Issue link:

What this PR does:

• Adds a new mcp call

Additional information:

Thanks to @amin-nikanjam for his earlier PR attempt, which served as the foundation for this one.
For schema validation reasons, it turned out to be simpler to restart from scratch rather than build on top of his implementation.

[Copilot]

Pull Request Overview

This PR adds support for Model Context Protocol (MCP) calls to the workflow specification, enabling workflows to interact with MCP servers through HTTP or STDIO transports.

• Introduces a new CallMCP task type with protocol version, method, parameters, timeout, transport, and client configuration
• Adds comprehensive documentation for MCP calls, transports (HTTP and STDIO), and client configuration
• Provides example implementations demonstrating MCP integration with Slack

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
schema/workflow.yaml	Defines the schema for the new MCP call task type including transport options and client configuration
dsl-reference.md	Documents the MCP call feature with usage examples and describes HTTP/STDIO transport configurations

Comments suppressed due to low confidence (1)

dsl-reference.md:1

• Corrected spelling of 'sttring' to 'string'.

# Serverless Workflow DSL - Reference

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