Refactor reverse proxy and enhance API routing

- Replaced the existing reverse proxy implementation with a new alias forwarding mechanism, improving path handling and request normalization.
- Updated the gateway to utilize the new forwarding approach, ensuring consistent handling of API requests and proper error management.
- Enhanced tests to validate the new routing behavior, including handling of double slashes and user endpoint requests.
- Improved documentation in GATEWAY_RUN.md to clarify the updated API routing and configuration requirements.

internal/aggregate/fetch.go

@@ -7,10 +7,10 @@ import (
 	"io"
 	"net/http"
 	"net/url"
-	"strings"
 	"time"
 
 	"github.com/telemt/telemt-api/internal/config"
+	"github.com/telemt/telemt-api/internal/proxy"
 )
 
 const statsUsersPath = "stats/users"
@@ -42,7 +42,7 @@ func FetchTelemtGET[T any](ctx context.Context, client *http.Client, parsed *con
 	if err != nil {
 		return zero, UpstreamCallMeta{OK: false, Error: err.Error()}
 	}
-	target := joinPathPrefix(u, srv.PathPrefix, relPath)
+	target := proxy.JoinPathPrefix(u, srv.PathPrefix, relPath)
 	start := time.Now()
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, target.String(), nil)
 	if err != nil {
@@ -102,28 +102,6 @@ func FetchStatsUsers(ctx context.Context, client *http.Client, parsed *config.Pa
 	return out
 }
 
-func joinPathPrefix(base *url.URL, pathPrefix, rest string) *url.URL {
-	rel := strings.Trim(pathPrefix, "/")
-	if rest != "" {
-		if rel != "" {
-			rel = rel + "/" + rest
-		} else {
-			rel = rest
-		}
-	}
-	var parts []string
-	for _, seg := range strings.Split(rel, "/") {
-		if seg != "" {
-			parts = append(parts, seg)
-		}
-	}
-	if len(parts) == 0 {
-		out := *base
-		return &out
-	}
-	return base.JoinPath(parts...)
-}
-
 func truncate(s string, n int) string {
 	if len(s) <= n {
 		return s