feat: Add creds for GitHub auth, add "none" auth to publisher (#276)

## Motivation and Context

- Adds credentials for the new MCP Registry Login GitHub Apps (local,
staging, prod)
- Adds support for "none" auth to publisher

## How Has This Been Tested?

- Tested publisher workflows locally
- Unit and integration tests passing

## Breaking Changes

None

## 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)
- [x] New feature (non-breaking change which adds functionality)
- [ ] 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. -->
- [x] I have read the [MCP
Documentation](https://modelcontextprotocol.io)
- [x] My code follows the repository's style guidelines
- [x] New and existing tests pass locally
- [x] I have added appropriate error handling
- [x] I have added or updated documentation as needed

---

Merging based on Tadas's approval review, and only making minor docs changes on top of that.

tests/integration/main.go

@@ -85,10 +85,10 @@ func run() error {
 		log.Fatalf("failed to get anonymous token: %v", err)
 	}
 
-	if err := os.WriteFile(".mcpregistry_token", []byte(token), 0600); err != nil {
+	if err := os.WriteFile(".mcpregistry_registry_token", []byte(token), 0600); err != nil {
 		log.Fatalf("failed to write token: %v", err)
 	}
-	defer os.Remove(".mcpregistry_token")
+	defer os.Remove(".mcpregistry_registry_token")
 
 	return publish(examples)
 }
@@ -121,7 +121,7 @@ func publish(examples []example) error {
 
 		ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
 		defer cancel()
-		cmd := exec.CommandContext(ctx, "./bin/publisher", "publish", "--mcp-file", p, "--registry-url", registryURL)
+		cmd := exec.CommandContext(ctx, "./bin/publisher", "publish", "--mcp-file", p, "--registry-url", registryURL, "--auth-method", "none")
 		cmd.WaitDelay = 100 * time.Millisecond
 
 		out, err := cmd.CombinedOutput()

tests/integration/run.sh

@@ -15,8 +15,6 @@ docker build -t registry .
 
 trap cleanup EXIT
 
-export MCP_REGISTRY_GITHUB_CLIENT_ID=fake
-export MCP_REGISTRY_GITHUB_CLIENT_SECRET=fake
 docker compose -f docker-compose.yml -f tests/integration/docker-compose.integration-test.yml up --wait --wait-timeout 60
 
 go run tests/integration/main.go