Investigate legacy dockerfile issues

[elstoc]

The following warnings were seen when using docker-compose to build ecms:

 => WARN: StageNameCasing: Stage name 'BUILDER' should be lowercase (line 1)                                                                                                                                                      0.0s
 => WARN: LegacyKeyValueFormat: "ENV key=value" should be used instead of legacy "ENV key value" format (line 2)                                                                                                                  0.0s
 => WARN: WorkdirRelativePath: Relative workdir "./app" can have unexpected results if the base image changes (line 8)                                                                                                            0.0s