Reject uploading existing version of maven artifacts

Problem to solve

Add switch to accept or deny uploading artifacts of existing version in maven.

Target audience

Loblaw's Release Engineering gitlab-ce~9335209

Further details

• Currently during our publish process we are downloading the maven-metadata.xml, loop through all available versions & if any matches with the current version(about to be published) we are terminating the process with non-zero. This has to be handled in GitLab Maven.
• Maven repo(at least jFrog) provides authority to deny uploading artifacts of same version.
• Only Admin or User with read, write, DELETE access can overwrite.

Relates to gitlab-ce#52710