Database version in features (#5627)

* adding database.version in the serverInfo (only MongoDB, it gives undefined when using Postgres)

* . correction of old 'features' tests
. adding engine and database in the StorageAdapter interface and implementations

* . version retrieval done in performInitialization
. PostgreSQL version

* performInitialization now returns a Promise

src/Adapters/Storage/StorageAdapter.js

@@ -25,6 +25,8 @@ export type FullQueryOptions = QueryOptions & UpdateQueryOptions;
 
 export interface StorageAdapter {
   canSortOnJoinTables: boolean;
+  databaseVersion: string;
+  engine: string;
 
   classExists(className: string): Promise<boolean>;
   setClassLevelPermissions(className: string, clps: any): Promise<void>;