Add reference to getting started guide and roadmap in how-to-release guide
OGM-701 [MongoDB] Minor refactoring
OGM-701 [MongoDB] Use MongoDBCredentials for authentication
OGM-701 [MongoDB] Create database only if create_database property is set
OGM-701 [MongoDB] Create property to select the authentication mechanism
OGM-701 [MongoDB] Document authorization mechanis property
OGM-701 [MongoDB] Document create_database property
OGM-701 [MongoDB] Minor fixes