Feature: Private API Gateway

[haowjern]

Overview

Added new configuration, inputs and outputs to allow us to create a Private API Gateway.

Proposed changes

• Add an IAM policy to be used when a private API is specified
  • At the moment, I can't update the policy to operate on specific resources because of the below reasons, so I have instead defined it to operate on all resource paths (which should be OK anyways)
    • Private API Gateway requires a 'policy' input, but I want to use this api gateway's ARN in the policy, but I can only get that once it is deployed, so there's a cyclic dependency here.
    • There's an open issue that might see changes introduced to fix this.
• Add configuration, inputs and outputs.

Notes

• This works in DEV, I'm able to create and connect to the private API Gateway

Tickets

• [SL-696]

Checklist

• Clear title such as "Feature: ..." or "Fix: ..." or other
• Clear and descriptive overview explaining why this change is needed
• List of changes proposed in this pull request (short bullet points)
• List of related changes such as external diffs, related releases or other
• Additional notes that would help the reviewers approve more quickly and with confidence

[crixey]

Looks pretty good to me