Cleaner ReleaseType parsing from project properties

[kikugie]

Motivation

This makes ReleaseType class accessible in build configuration, so setup like this is possible: gradle.properties

# ... 
release_type=stable

build.gradle

import me.modmuss50.mpp.ReleaseType
// ...
publishMods {
    type = ReleaseType.of(project.release_type)
    // ...
}

Current behaviour

Currently this can be replicated this way: build.gradle

import me.modmuss50.mpp.PublishOptions
// ...
publishMods {
    type = PublishOptions.ReleaseType.valueOf(project.release_type.toUpperCase())
    // ...
}

This approach includes more boilerplate and has a less descriptive error message.

[modmuss50]

Looks good, make sure to run spotlessKotlin and spotlessKotlinApply Gradle tasks so the build passes 👍