Allow Custom Endpoint URL Assignment via AWS ALB

[freeformflow]

Right now we default to having a CloudFront distribution in front of Gateway, but it has problems:

1. It's really slow the first time you deploy and when you teardown
2. It requires the developer to go get an ACM cert

The release of ALB yesterday gives us another, much faster option to provide URL assignment.

So the expected scheme is to:

• If no custom domain is provided: the CLI outputs the Gateway's default URL https://{distributionID}.execute-api.{region}.amazonaws.com/{stageName}
• If a custom domain is provided, but no caching is requested: Panda Sky deploys with ALB (with or without TLS)
• If a custom domain is provided, and caching is requested: Panda Sky deploys with a CFr distro (TLS cert required)

[freeformflow]

ALB integration isn't possible... yet. ALBs can only create listeners for endpoints from within a VPC, and Gateway does not support VPC integration.

I'm moving this to future. If either of these restrictions change, we'll be able to move on this, but not today. 😕