feature(database-connection): First implementation

backend/src/app.module.ts

@@ -2,10 +2,11 @@ import { Module } from '@nestjs/common';
 import { AppController } from './app.controller';
 import { AppService } from './app.service';
 import { SinusBotService } from "./services/sinusbot.service";
+import { DatabaseService } from './database/database.service';
 
 @Module({
   imports: [],
   controllers: [AppController],
-  providers: [AppService, SinusBotService],
+  providers: [AppService, SinusBotService, DatabaseService],
 })
 export class AppModule {}