Implement Mongo Seeder v2

What does this MR do?

Adds seeding to User and Questions databases with following env variables to control it:

• ENABLE_QUESTION_DB_SEEDING.
• ENABLE_USER_DB_SEEDING.

Testing

• Ensure ENABLE_QUESTION_DB_SEEDING is set to true in docker-compose.
• Ensure ENABLE_USER_DB_SEEDING is set to true in docker-compose.
• Ensure Docker's MongoDB instances have no documents in Users and Questions DBs.
• Run docker compose up --build.
• Login as with username 'admin' and password 'password'.
• Question appears on page.

Relevant issues

Fixes missing seeding.

backend-services/feed-service/app/ApplicationStart.scala

+import scala.concurrent.Future
+import javax.inject._
+import play.api.inject.ApplicationLifecycle
+
+import utils.ConfigHelper
+import repositories.QuestionRepository
+
+// Creates an `ApplicationStart` object once at start-up and registers hook for shut-down.
+@Singleton
+class ApplicationStart @Inject() (lifecycle: ApplicationLifecycle) {
+  println("Starting...")
+
+  if (ConfigHelper.getBoolean("enable.question.db.seeding")) {
+    QuestionRepository.seedDatabase()
+  }
+
+  // Shut-down hook
+  lifecycle.addStopHook { () =>
+    Future.successful(())
+  }
+}