MM-60171: Using a generic function to allocate values (#28245)

We sprinkle a bit of generic magic to refactor a lot
of duplicate code.

To avoid exposing unnecessary code, I duplicated the function
twice. But let me know if you have strong opinions about this.

https://mattermost.atlassian.net/browse/MM-60171

```release-note
NONE
```


---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/app/platform/utils.go

@@ -20,3 +20,13 @@ func maxInt(a, b int) int {
 	}
 	return b
 }
+
+// allocateCacheTargets is used to fill target value types
+// for getting items from cache.
+func allocateCacheTargets[T any](l int) []any {
+	toPass := make([]any, 0, l)
+	for i := 0; i < l; i++ {
+		toPass = append(toPass, new(T))
+	}
+	return toPass
+}