MM-43143: Dataloaders for roles (#19936)

We use a dataloader to optimize roles loading.

https://mattermost.atlassian.net/browse/MM-43143

```release-note
NONE
```

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

go.mod

@@ -41,6 +41,7 @@ require (
 	github.com/gorilla/mux v1.8.0
 	github.com/gorilla/schema v1.2.0
 	github.com/gorilla/websocket v1.5.0
+	github.com/graph-gophers/dataloader/v6 v6.0.0
 	github.com/graph-gophers/graphql-go v1.3.0
 	github.com/h2non/go-is-svg v0.0.0-20160927212452-35e8c4b0612c
 	github.com/hako/durafmt v0.0.0-20210608085754-5c1018a4e16b
@@ -51,7 +52,6 @@ require (
 	github.com/hashicorp/go-multierror v1.1.1 // indirect
 	github.com/hashicorp/go-plugin v1.4.3
 	github.com/hashicorp/go-sockaddr v1.0.2 // indirect
-	github.com/hashicorp/golang-lru v0.5.4 // indirect
 	github.com/hashicorp/memberlist v0.3.1
 	github.com/hashicorp/yamux v0.0.0-20211028200310-0bc27b27de87 // indirect
 	github.com/jaytaylor/html2text v0.0.0-20211105163654-bc68cce691ba