Introduce v0.1 version of the API (#658)

<!-- 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 v0.1 API version. 

The goal is to mark v0.1 as a "freeze" point while keeping v0 as the
moving target for new features so integrators can start building on top
of something stable(r).

Details:
* This change is quite simple - we re-register the same handlers twice,
once as `v0` and once as `v0.1`
* Going forward, we'll keep v0.1 frozen while we add changes either on
top of both (non-breaking) or we'll have to branch if breaking changes
are necessary
* We all acknowledge this is not exactly best-practice, but it gives us
a way to gather feedback and allow clients to start integrating with the
API without breaking them (**note** this implies a follow up PR that
would branch the handlers used in v0.1).
* For integrators/clients: please provide your feedback - what works
well, what doesn't so we can take this into account going towards GA.

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

## Breaking Changes
<!-- Will users need to update their code or configurations? -->
No, this just adds a new API version alongside the existing one.

## 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)
- [ ] 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
-->
Fixes: #649

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

internal/api/router/router.go

@@ -102,9 +102,10 @@ func handle404(w http.ResponseWriter, r *http.Request) {
 	detail := "Endpoint not found. See /docs for the API documentation."
 
 	// Provide suggestions for common API endpoint mistakes
-	if !strings.HasPrefix(path, "/v0/") {
+	if !strings.HasPrefix(path, "/v0/") && !strings.HasPrefix(path, "/v0.1/") {
 		detail = fmt.Sprintf(
-			"Endpoint not found. Did you mean '%s'? See /docs for the API documentation.",
+			"Endpoint not found. Did you mean '%s' or '%s'? See /docs for the API documentation.",
+			"/v0.1"+path,
 			"/v0"+path,
 		)
 	}
@@ -145,6 +146,7 @@ func NewHumaAPI(cfg *config.Config, registry service.RegistryService, mux *http.
 
 	// Register routes for all API versions
 	RegisterV0Routes(api, cfg, registry, metrics)
+	RegisterV0_1Routes(api, cfg, registry, metrics)
 
 	// Add /metrics for Prometheus metrics using promhttp
 	mux.Handle("/metrics", metrics.PrometheusHandler())

internal/api/router/v0.go

@@ -14,10 +14,21 @@ import (
 func RegisterV0Routes(
 	api huma.API, cfg *config.Config, registry service.RegistryService, metrics *telemetry.Metrics,
 ) {
-	v0.RegisterHealthEndpoint(api, cfg, metrics)
-	v0.RegisterPingEndpoint(api)
-	v0.RegisterServersEndpoints(api, registry)
-	v0.RegisterEditEndpoints(api, registry, cfg)
-	v0auth.RegisterAuthEndpoints(api, cfg)
-	v0.RegisterPublishEndpoint(api, registry, cfg)
+	v0.RegisterHealthEndpoint(api, "/v0", cfg, metrics)
+	v0.RegisterPingEndpoint(api, "/v0")
+	v0.RegisterServersEndpoints(api, "/v0", registry)
+	v0.RegisterEditEndpoints(api, "/v0", registry, cfg)
+	v0auth.RegisterAuthEndpoints(api, "/v0", cfg)
+	v0.RegisterPublishEndpoint(api, "/v0", registry, cfg)
+}
+
+func RegisterV0_1Routes(
+	api huma.API, cfg *config.Config, registry service.RegistryService, metrics *telemetry.Metrics,
+) {
+	v0.RegisterHealthEndpoint(api, "/v0.1", cfg, metrics)
+	v0.RegisterPingEndpoint(api, "/v0.1")
+	v0.RegisterServersEndpoints(api, "/v0.1", registry)
+	v0.RegisterEditEndpoints(api, "/v0.1", registry, cfg)
+	v0auth.RegisterAuthEndpoints(api, "/v0.1", cfg)
+	v0.RegisterPublishEndpoint(api, "/v0.1", registry, cfg)
 }