MM-10264: Adds CLI command to import and export permissions. (#8787)

* MM-10264: Adds CLI command to import and export permissions.

* MM-10264: Changes Scheme Name to DisplayName and adds Name slug field.

* MM-10264: Changes display name max size.

* MM-10264: Another merge fix.

* MM-10264: Changes for more Schemes methods checking for migration.

* MM-10264: More updates for Schemes migration checking.

app/scheme.go

@@ -4,8 +4,10 @@
 package app
 
 import (
-	"github.com/mattermost/mattermost-server/model"
 	"net/http"
+
+	"github.com/mattermost/mattermost-server/model"
+	"github.com/mattermost/mattermost-server/store"
 )
 
 func (a *App) GetScheme(id string) (*model.Scheme, *model.AppError) {
@@ -146,3 +148,15 @@ func (a *App) IsPhase2MigrationCompleted() *model.AppError {
 
 	return nil
 }
+
+func (a *App) SchemesIterator(batchSize int) func() []*model.Scheme {
+	offset := 0
+	return func() []*model.Scheme {
+		var result store.StoreResult
+		if result = <-a.Srv.Store.Scheme().GetAllPage("", offset, batchSize); result.Err != nil {
+			return []*model.Scheme{}
+		}
+		offset += batchSize
+		return result.Data.([]*model.Scheme)
+	}
+}