app: use relative paths instead of absolute paths for the supported http handlers on the main page

This allows hiding VictoriaMetrics components behind proxies, which serve pages at different path prefixes

See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/1858

lib/httpserver/httpserver.go

@@ -13,7 +13,6 @@ import (
 	"net/http"
 	"net/http/pprof"
 	"os"
-	"path"
 	"runtime"
 	"strconv"
 	"strings"
@@ -637,7 +636,6 @@ func GetPathPrefix() string {
 func WriteAPIHelp(w io.Writer, pathList [][2]string) {
 	for _, p := range pathList {
 		p, doc := p[0], p[1]
-		p = path.Join(*pathPrefix, p)
 		fmt.Fprintf(w, "<a href=%q>%s</a> - %s<br/>", p, p, doc)
 	}
 }