Publishing to Gradle portal

[vondacho]

Need: to use the plugin inside a Gradle script with Kotlin DSL.

Example: plugins { id("net.serenity-bdd.gradle").version("2.4.24") }

Proposal (I am missing permissions for submitting a pull request):

gradlePlugin {
    plugins {
        serenityPlugin {
            id = 'net.serenity-bdd.gradle'
            displayName = 'Serenity BDD Cucumber 6 Integration'
            description = 'Run Serenity tests and generate Serenity reports using Cucumber 6'
            implementationClass = 'net.serenitybdd.plugins.gradle.SerenityPlugin'
        }
    }
}

pluginBundle {
    website = 'https://github.com/serenity-bdd/serenity-gradle-plugin'
    vcsUrl = 'https://github.com/serenity-bdd/serenity-gradle-plugin.git'
    tags = ['cucumber', 'serenity', 'tests', 'reporting', 'livingdocumentation']
}

See publishing_gradle_plugins

* To upload a new release to Gradle portal:
* gradle clean publishPlugins -PcoreRelease -Pgradle.publish.key=<key> -Pgradle.publish.secret=<secret>

See PR: #4