Some performance optimization on dashboard and issues page (#29010)

This PR do some loading speed optimization for feeds user interface
pages.
- Load action users batchly but not one by one.
- Load action repositories batchly but not one by one.
- Load action's Repo Owners batchly but not one by one.
- Load action's possible issues batchly but not one by one.
- Load action's possible comments batchly but not one by one.

modules/util/slice.go

@@ -53,3 +53,12 @@ func Sorted[S ~[]E, E cmp.Ordered](values S) S {
 	slices.Sort(values)
 	return values
 }
+
+// TODO: Replace with "maps.Values" once available
+func ValuesOfMap[K comparable, V any](m map[K]V) []V {
+	values := make([]V, 0, len(m))
+	for _, v := range m {
+		values = append(values, v)
+	}
+	return values
+}