cmd/utils: keep metrics tag values containing '='

SplitTagsFlag split each "k=v" tag on every "=" with strings.Split,
producing more than two parts whenever the value itself contained an
"=" (e.g. build=release=2026). Such a tag failed the len(kv) == 2 check
and was silently dropped.

Use strings.SplitN(t, "=", 2) so the split happens only on the first
"=", keeping the remainder as the value. A tag list like
'host=node1,build=release=2026' now retains the build tag.

cmd/utils/flags.go

@@ -2268,7 +2268,7 @@ func SplitTagsFlag(tagsFlag string) map[string]string {
 
 	for _, t := range tags {
 		if t != "" {
-			kv := strings.Split(t, "=")
+			kv := strings.SplitN(t, "=", 2)
 
 			if len(kv) == 2 {
 				tagsMap[kv[0]] = kv[1]