Export Cube's data model as artifact

Creating this feature request based on conversation in Slack.

**Is your feature request related to a problem? Please describe.**
From Slack convo, original problem -

> We use the CDK for provisioning, does Cube expose the schema definitions in a way that would allow us to import them into the infrastructure code? It could make base queries in Quicksights a lot less brittle.

Generally, the ability to export Cube's data model as an artifact will increase interoperability with other tools and will enable more semantic layer integrations.

**Describe the solution you'd like**
A command that can be used executed during the CI process and export JSON-based artificat with descriptions of Cube's data model.

**Describe alternatives you've considered**
Spin up Cube during the CI process and hit `/meta` endpoint.