fix: allow custom helper helpers to be defined in main template

Before, you could only use {{- define "foo" }} blocks inside file
that was brought through the "--include" flag. This change makes it
so that the main template file itself is also made part of the
include list automatically. This way any helper templates that are
defined there can also be called directly using the {{- include "foo" }}
mechanism.

feat: add support for Terraform HCL format

With the new transform commands you should be able to go back and forth
between Terraform HCL and JSON. The transform between these two formats
adheres to the rules specified at:
  https://developer.hashicorp.com/terraform/language/syntax/json

  * transform tf-to-json
    Converts input Terraform HCL into HCL JSON
  * transform json-to-tf
    Converts input JSON into Terraform HCL

There is also a new flag (--set-tf) that can be passed to the render commands.
This flag works the same way as the other flags in the same family.

  --set-tf context_key=./path/to/terraform/file.tf

The input Terraform HCL file is converted to JSON format and made
available in the context as a map[string]any.

feat: add support for image and audio formats in tool responses

Also, add support for other common binary data responses.
These are included as embedded binary resources in the tool response.

feat: add support for server-side tool filter on MCP API proxy

This feature allows client to pass a header `x-mcp-tools-filter`
when calling the `tools/list`. The filter is a comma separated
list of tools that the client wants to see in the tools/list response.

This is useful for showing only a subset of tools to an LLM and avoiding
context rot.

Also, modify the implementation of for API product authorization based filtering to
use a simple comma separated list as well, and be consistent with tools filtering.

feat: add MCP API Key auth and API Product authorization

Add robust authentication and authorization capabilities to the MCP template.
* Use VerifyAPIKey policy for authentication.
* Use API Product for governance / granular tool level authorization.

docs: update MCP docs to describe the MCP template features

docs: add doc page showing how to MCPfy a REST API

Merge pull request #34 from apigee/mcp-updates

Some MCP fixes, and support for XML and URL-Encoded request body

feat: add support for generating MCP API Proxy from spec

chore: use upload-artifact@v4 for release workflow