Reflect the latest registry changes in openapi.yaml (#345)

<!-- Provide a brief summary of your changes -->

## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
The following PR:
* Adds a new `transport` type used in Package and Remotes
* Added `docker` to the `runtime_hint` examples
* Added support for templated URLs. It is available for streamable-http
and sse transports for Packages. I didn't thought of reasons to have
this for Remotes, but we can enable it if needed.
* Added validation for templated URLs so we can ensure all referenced
placeholder variables are available.
* For streamable-http and SSE transport types the URL is now a required
property
* Updated the publisher init command to reflect these changes
* Updated the seed.json file
* Added unit tests for the transport type related changes
* Updated the server.json schema and the external pkg structs to reflect
the new transport type
* Updated the examples

Thanks to @kkkarthik for spotting it! 🙏 

## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->
Ran the tests locally

## Breaking Changes
<!-- Will users need to update their code or configurations? -->
Yes

## Types of changes
<!-- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->
- [ ] Bug fix (non-breaking change which fixes an issue)
- [ ] New feature (non-breaking change which adds functionality)
- [x] Breaking change (fix or feature that would cause existing
functionality to change)
- [ ] Documentation update

## Checklist
<!-- Go over all the following points, and put an `x` in all the boxes
that apply. -->
- [ ] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [ ] 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
<!-- Add any other context, implementation notes, or design decisions
-->

---------

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>

internal/validators/validators.go

@@ -34,7 +34,7 @@ func ValidateServerJSON(serverJSON *apiv0.ServerJSON) error {
 
 	// Validate all remotes
 	for _, remote := range serverJSON.Remotes {
-		if err := validateRemote(&remote); err != nil {
+		if err := validateTransport(&remote); err != nil {
 			return err
 		}
 	}
@@ -81,6 +81,12 @@ func validatePackageField(obj *model.Package) error {
 		}
 	}
 
+	// Validate transport with template variable support
+	availableVariables := collectAvailableVariables(obj)
+	if err := validatePackageTransport(&obj.Transport, availableVariables); err != nil {
+		return fmt.Errorf("invalid transport: %w", err)
+	}
+
 	return nil
 }
 
@@ -130,11 +136,83 @@ func validateArgumentValueFields(name, value, defaultValue string) error {
 	return nil
 }
 
-func validateRemote(obj *model.Remote) error {
-	if !IsValidURL(obj.URL) {
-		return fmt.Errorf("%w: %s", ErrInvalidRemoteURL, obj.URL)
+// collectAvailableVariables collects all available template variables from a package
+func collectAvailableVariables(pkg *model.Package) []string {
+	var variables []string
+	
+	// Add environment variable names
+	for _, env := range pkg.EnvironmentVariables {
+		variables = append(variables, env.Name)
+	}
+	
+	// Add runtime argument names and value hints
+	for _, arg := range pkg.RuntimeArguments {
+		if arg.Name != "" {
+			variables = append(variables, arg.Name)
+		}
+		if arg.ValueHint != "" {
+			variables = append(variables, arg.ValueHint)
+		}
+	}
+	
+	// Add package argument names and value hints
+	for _, arg := range pkg.PackageArguments {
+		if arg.Name != "" {
+			variables = append(variables, arg.Name)
+		}
+		if arg.ValueHint != "" {
+			variables = append(variables, arg.ValueHint)
+		}
+	}
+	
+	return variables
+}
+
+// validatePackageTransport validates a package's transport with templating support
+func validatePackageTransport(transport *model.Transport, availableVariables []string) error {
+	// Validate transport type is supported
+	switch transport.Type {
+	case model.TransportTypeStdio:
+		// No additional validation needed for stdio - URL should be empty
+		return nil
+	case model.TransportTypeStreamableHTTP, model.TransportTypeSSE:
+		// URL is required for streamable-http and sse
+		if transport.URL == "" {
+			return fmt.Errorf("url is required for %s transport type", transport.Type)
+		}
+		// Validate URL format with template variable support
+		if !IsValidTemplatedURL(transport.URL, availableVariables, true) {
+			// Check if it's a template variable issue or basic URL issue
+			templateVars := extractTemplateVariables(transport.URL)
+			if len(templateVars) > 0 {
+				return fmt.Errorf("%w: template variables in URL %s reference undefined variables. Available variables: %v", 
+					ErrInvalidRemoteURL, transport.URL, availableVariables)
+			}
+			return fmt.Errorf("%w: %s", ErrInvalidRemoteURL, transport.URL)
+		}
+		return nil
+	default:
+		return fmt.Errorf("unsupported transport type: %s", transport.Type)
+	}
+}
+
+// validateTransport validates a remote transport (no templating allowed)
+func validateTransport(obj *model.Transport) error {
+	// Validate transport type is supported - remotes only support streamable-http and sse
+	switch obj.Type {
+	case model.TransportTypeStreamableHTTP, model.TransportTypeSSE:
+		// URL is required for streamable-http and sse
+		if obj.URL == "" {
+			return fmt.Errorf("url is required for %s transport type", obj.Type)
+		}
+		// Validate URL format (no templates allowed for remotes, no localhost)
+		if !IsValidRemoteURL(obj.URL) {
+			return fmt.Errorf("%w: %s", ErrInvalidRemoteURL, obj.URL)
+		}
+		return nil
+	default:
+		return fmt.Errorf("unsupported transport type for remotes: %s (only streamable-http and sse are supported)", obj.Type)
 	}
-	return nil
 }
 
 // ValidatePublishRequest validates a complete publish request including extensions