Allow providing release and snapshot repositories

[x] All tests passed. If this feature is not already covered by the tests, I added new tests.

Resolves https://github.com/jfrog/artifactory-gradle-plugin/issues/47 Resolves https://github.com/jfrog/artifactory-gradle-plugin/issues/97

Option 1: Let the plugin decide which to repository to publish the artifacts to by allowing the provision of both snapshot and release repositories.

configure<ArtifactoryPluginConvention> {
    publish {
        repoKey = "libs-snapshot-local"
    }
}

artifactory {
    publish {
        repository {
            repoKey = "libs-snapshot-local"
        }
    }
}

Option 2 (new):

configure<ArtifactoryPluginConvention> {
    publish {
            releaseRepoKey = "libs-release-local"
            snapshotRepoKey = "libs-snapshot-local"
    }
}

artifactory {
    publish {
        repository {
             releaseRepoKey = 'libs-release-local'
             snapshotRepoKey = 'libs-snapshot-local'
        }
    }
}

jfrog / artifactory-gradle-plugin

Allow providing release and snapshot repositories #100