Remove use of groovy scripts where possible

[thiagofigueiro]

From Nexus 3.21.2, scripting is disabled by default. When nexus3-cli was first created, the REST API didn't have much to offer so a lot of the functionality depends on groovy scripts.

The REST API has been continuously improved and, these days, it might be possible to achieve most of what we need using it.

This issue is to discover which features can be done using the REST API and write some issues to replace the groovy script with an API implementation. This should be done for versions that support the required API calls - we might choose to keep the groovy scripts around for older versions, at least in the short-medium term.

See: https://support.sonatype.com/hc/en-us/articles/360045220393-Scripting-Nexus-Repository-Manager-3