Smart cleanup of docker images in Sonatype Nexus OSS Repository

This script keeps last retentionCount versions of each build type of each docker image, while doesn't touch versions younger than retentionDays at all.

Build type (i.e. dev, stage, prod) is determined from image tag with use of pattern.

If build type is not found in image tag, script tries to interpret the tag with SemVer notation and extract build type from SemVer label.

• Add this script to Nexus Tasks with type "Admin - Execute script".
• Set retentionDays, retentionCount, whitelist params.
• Set pattern and patternSemver params if appropriate.
• Alter retentions params for specific repos with alterRetention.

Uncomment service.deleteComponent line to proceed with deletion.

Don't forget to execute "Docker - Delete unused manifests and images" and "Admin - Compact blob store" tasks after the script.