GraphQL: Unlock goroutine throttle to match batch capacity (#20146)

We were throttling the amount of concurrent resolvers
at a given time. The idea behind this was to avoid overloading
the database with too many requests.

However, with the introduction of dataloaders, this limitation
actually becomes a bottleneck because all DB calls are actually
batched, so we are unnecessarily throttling the amount of
items that can be processed in a single batch.

The only caveat with this is that now all resolvers
need to backed by dataloaders, or otherwise not be queried
as part of a loop.

In a subsequent PR, we will be removing channel stats
from under channel to be a top-level object to be returned
for a given channel.

```release-note
NONE
```

app/user.go

@@ -380,6 +380,15 @@ func (a *App) GetUser(userID string) (*model.User, *model.AppError) {
 	return user, nil
 }
 
+func (a *App) GetUsers(userIDs []string) ([]*model.User, *model.AppError) {
+	users, err := a.ch.srv.userService.GetUsers(userIDs)
+	if err != nil {
+		return nil, model.NewAppError("GetUsers", "app.user.get.app_error", nil, err.Error(), http.StatusInternalServerError)
+	}
+
+	return users, nil
+}
+
 func (a *App) GetUserByUsername(username string) (*model.User, *model.AppError) {
 	result, err := a.ch.srv.userService.GetUserByUsername(username)
 	if err != nil {
@@ -426,8 +435,8 @@ func (a *App) GetUserByAuth(authData *string, authService string) (*model.User,
 	return user, nil
 }
 
-func (a *App) GetUsers(options *model.UserGetOptions) ([]*model.User, *model.AppError) {
-	users, err := a.ch.srv.userService.GetUsers(options)
+func (a *App) GetUsersFromProfiles(options *model.UserGetOptions) ([]*model.User, *model.AppError) {
+	users, err := a.ch.srv.userService.GetUsersFromProfiles(options)
 	if err != nil {
 		return nil, model.NewAppError("GetUsers", "app.user.get_profiles.app_error", nil, err.Error(), http.StatusInternalServerError)
 	}