Implement toNode for partition models

[ganeshnj]

Issue #, if available:

Description of changes:

Motivation

Currently I'm relying on the internal APIs to get the node for partitions in Swift SDK which we must not given how partitions are managed is totally internal details.

val partitions = DefaultPartitionDataProvider::class.java.getResourceAsStream("/software/amazon/smithy/rulesengine/language/partitions.json")
writer.write("private let partitions = \$S", Node.printJson(Node.parse(partitions)))

Changes

This change makes Parititions class Node convertible.

Result

I could do

val partitions = DefaultPartitionDataProvider().loadPartitions()
writer.write("private let partitions = \$S", Node.printJson(partitions.toNode()))

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[JordonPhillips]

Lets add a quick test case please

[ganeshnj]

Lets add a quick test case please

Added one.