[Suggestion] Add shadow plugin to UMC mods

[Goldenfield192]

Need discussion
Add shadow plugin in template buildscript ad something like this in umc.json

//inside mod block
        "libraries" : [
            {
                "repository": "maven repo",
                "artifact": "groovy short format, like net.neoforged.gradleutils:GradleUtils:3.0.0-alpha.4-SNAPSHOT",
                "type": "runtime/shadow",
                "relocate" : "if shadow enabled, set true to shadow into pkg.shade",
                "relocated_package" : "if shadow enabled, which package to relocate?",
                "only_in" : [
                    "e.g. 1.12.2-forge","1.20.1-forge"
                ]
            }
        ]