Allow for vendor extensions on servers (#298)

<!-- Provide a brief summary of your changes -->
This PR serves as a placeholder and brings together all of the changes
related to supporting vendor extensions passed through the API. The idea
is to have a single place to track and review the work as it comes
together (even if it’s still a bit of a work in progress).

**The changes in this PR cover:**
* Updates on the data model
* Updates on both databases (in-memory and postgresql), added a new
table to PSQL for tracking the extensions leaving the server table only
for the clean server.json properties
* Updates the seed.json file (thus the big line change)
* Adds a seed-migrate tool to help migrating an existing seed file to
the new format
* Updates the seed import mechanism to support this
* Updates the existing tests - unit, integration and validation tests
* Adds the publish handler to the OpenAPI spec (it was missing)
* Fixes linting errors
* Updates on the API side on (publish, list, get) to support the new
format of `ServerResponse` -
```
{
  "server": {},
  "x-io.modelcontextprotocol.registry": {}, /*not available for publish since this gets populated by the registry*/
  "x-publisher": {}
}
```

## Motivation and Context
<!-- Why is this change needed? What problem does it solve? -->
Motivated by the discussions in:
https://github.com/modelcontextprotocol/registry/discussions/284

## How Has This Been Tested?
<!-- Have you tested this in a real application? Which scenarios were
tested? -->
Locally and by running all of the tests

## Breaking Changes
<!-- Will users need to update their code or configurations? -->
Yes, it changes both the API and the format of the seed file
 
## 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

---

Signed-off-by: Radoslav Dimitrov <radoslav@stacklok.com>
Co-authored-by: adam jones <domdomegg+git@gmail.com>

tools/publisher/auth/dns.go

@@ -5,8 +5,7 @@ type DNSProvider struct {
 }
 
 // NewDNSProvider creates a new DNS-based auth provider
-//
-//nolint:ireturn
+//nolint:ireturn // Factory function returns interface by design
 func NewDNSProvider(registryURL, domain, hexSeed string) Provider {
 	return &DNSProvider{
 		CryptoProvider: &CryptoProvider{

tools/publisher/auth/github-at.go

@@ -63,7 +63,8 @@ type ServerHealthResponse struct {
 }
 
 // NewGitHubATProvider creates a new GitHub OAuth provider
-func NewGitHubATProvider(forceLogin bool, registryURL string) Provider { //nolint:ireturn
+//nolint:ireturn // Factory function returns interface by design
+func NewGitHubATProvider(forceLogin bool, registryURL string) Provider {
 	return &GitHubATProvider{
 		forceLogin:  forceLogin,
 		registryURL: registryURL,

tools/publisher/auth/github-oidc.go

@@ -14,7 +14,8 @@ type GitHubOIDCProvider struct {
 	registryURL string
 }
 
-func NewGitHubOIDCProvider(registryURL string) Provider { //nolint:ireturn
+//nolint:ireturn // Factory function returns interface by design
+func NewGitHubOIDCProvider(registryURL string) Provider {
 	return &GitHubOIDCProvider{
 		registryURL: registryURL,
 	}

tools/publisher/auth/http.go

@@ -5,8 +5,7 @@ type HTTPProvider struct {
 }
 
 // NewHTTPProvider creates a new HTTP-based auth provider
-//
-//nolint:ireturn
+//nolint:ireturn // Factory function returns interface by design
 func NewHTTPProvider(registryURL, domain, hexSeed string) Provider {
 	return &HTTPProvider{
 		CryptoProvider: &CryptoProvider{

tools/publisher/auth/none.go

@@ -19,7 +19,8 @@ type TokenResponse struct {
 	ExpiresAt     int64  `json:"expires_at"`
 }
 
-func NewNoneProvider(registryURL string) Provider { //nolint:ireturn
+//nolint:ireturn // Factory function returns interface by design
+func NewNoneProvider(registryURL string) Provider {
 	return &NoneProvider{
 		registryURL: registryURL,
 	}

tools/publisher/main.go

@@ -344,8 +344,17 @@ func publishToRegistry(registryURL string, mcpData []byte, token string) error {
 		return fmt.Errorf("error parsing server.json file: %w", err)
 	}
 
-	// Create the publish request payload (without authentication)
-	publishReq := mcpDetails
+	// Create the publish request payload
+	var publishReq map[string]any
+	if _, hasServerField := mcpDetails["server"]; hasServerField {
+		// Already in PublishRequest format with server field (and possibly x-publisher)
+		publishReq = mcpDetails
+	} else {
+		// Legacy ServerDetail format - wrap it in extension wrapper format
+		publishReq = map[string]any{
+			"server": mcpDetails,
+		}
+	}
 
 	// Convert the request to JSON
 	jsonData, err := json.Marshal(publishReq)