MM-62378: Initialize status and session cache before loading license (#29686)

* MM-62378: Initialize status and session cache before loading license

ps.LoadLicense could end up calling InvalidateAllCaches. Therefore,
we need to intialize those caches before calling LoadLicense
to prevent a panic from happening.

While here, we also remove some unused code.

https://mattermost.atlassian.net/browse/MM-62378
```release-note
NONE
```

* fix lint errors

```release-note
NONE
```

* fix test

```release-note
NONE
```

server/channels/app/platform/cluster_handlers.go

@@ -6,7 +6,6 @@ package platform
 import (
 	"bytes"
 	"encoding/json"
-	"fmt"
 
 	"github.com/mattermost/mattermost/server/public/model"
 	"github.com/mattermost/mattermost/server/public/shared/mlog"
@@ -31,19 +30,6 @@ func (ps *PlatformService) RegisterClusterMessageHandler(ev model.ClusterEvent,
 	ps.additionalClusterHandlers[ev] = h
 }
 
-// ClusterHandlersPreCheck checks whether the platform service is ready to handle cluster messages.
-func (ps *PlatformService) ClusterHandlersPreCheck() error {
-	if ps.Store == nil {
-		return fmt.Errorf("could not find store")
-	}
-
-	if ps.statusCache == nil {
-		return fmt.Errorf("could not find status cache")
-	}
-
-	return nil
-}
-
 func (ps *PlatformService) ClusterPublishHandler(msg *model.ClusterMessage) {
 	event, err := model.WebSocketEventFromJSON(bytes.NewReader(msg.Data))
 	if err != nil {