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/session.go

@@ -63,14 +63,9 @@ func (ps *PlatformService) ClearUserSessionCacheLocal(userID string) {
 			return nil
 		}
 
-		toPass := make([]any, 0, len(keys))
-		for i := 0; i < len(keys); i++ {
-			// This always needs to be a pointer to a value.
-			// Otherwise the msp unmarshaler will fail to work.
-			var session model.Session
-			toPass = append(toPass, &session)
-		}
-
+		// This always needs to be model.Session, not *model.Session.
+		// Otherwise the msp unmarshaler will fail to work.
+		toPass := allocateCacheTargets[model.Session](len(keys))
 		errs := ps.sessionCache.GetMulti(keys, toPass)
 		for i, err := range errs {
 			if err != nil {