Finished the maintenance messages and added container state

.../src/main/java/at/tuwien/endpoints/ContainerEndpoint.java

.../at/tuwien/endpoint/ContainerEndpointIntegrationTest.java

...va/at/tuwien/service/ContainerServiceIntegrationTest.java

...ces/src/main/java/at/tuwien/service/ContainerService.java

...ain/java/at/tuwien/service/impl/ContainerServiceImpl.java

...e/src/main/java/at/tuwien/endpoints/DatabaseEndpoint.java

...est/java/at/tuwien/endpoint/DatabaseEndpointUnitTest.java

...ervices/src/main/java/at/tuwien/config/GatewayConfig.java

.../main/java/at/tuwien/gateway/ContainerServiceGateway.java

...a/at/tuwien/gateway/impl/ContainerServiceGatewayImpl.java

...ces/src/main/java/at/tuwien/service/ContainerService.java

...ain/java/at/tuwien/service/impl/ContainerServiceImpl.java

...ava/at/tuwien/api/maintenance/BannerMessageCreateDto.java

...ava/at/tuwien/api/maintenance/BannerMessageUpdateDto.java

...tadata-db/test/src/main/java/at/tuwien/test/BaseTest.java

dbrepo-ui/components/DatabaseList.vue

dbrepo-ui/components/dialogs/EditMaintenanceMessage.vue

dbrepo-ui/layouts/default.vue

...es/container/_container_id/database/_database_id/info.vue

dbrepo-ui/utils/index.js