Diagram creation and export API

[grsr]

Feature name
Perspective diagram creating and export API

Is your feature request related to a problem? Please describe.
Currently creating an exporting diagrams is a manual process.

Describe the feature you'd like to see implemented
A mechanism to automatically create and export previously configured diagrams for use in electronic documentation, such as confluence.

Describe the value this feature will add to AWS Perspective
The requesting customer would like to automatically keep diagrams generate in Perspective and shared via other means up-to-date.

Describe alternatives you've considered
It might be possible to automate this with the existing UI with selenium scripts etc. but this seems brittle and error-prone.

[grsr]

This was a direct request from a customer considering deploying Perspective and comparing it with third-party offerings

[svozza]

We will be launching an SDK to allow programmatic access to the APIs that underlie the frontend: #399.