Refactor templates to have fewer imported values

[cat5inthecradle]

!ImportValue adds cross-stack dependencies and breaks the cleaner top-down passing of parameters. This PR eliminates !ImportValue from the application stack via two changes:

• The CICD pipeline stack tells the app stacks what VPC, security group, and subnets to use
• The app stack creates it's own ECS Task Execution Role

This also modifies the deploy scripts to create a change set which can be reviewed before applying.

Notes for reviewers - the shell script changes are independent of the template changes, but having them in place will make reviewing the template changes easier.

TESTING

• TODO deploy a both a dev environment and a prod-like pipeline to validate that the parameter overrides are formatting correctly.

Follow Up

• delete the now redundant ecs task execution role being created in the dependencies template AFTER all stacks are updated to use their own role.

[cat5inthecradle]

This is a tentative removal. I don't think we need it here. This stack is being deployed by an Admin anyway. I might be overlooking something though.