Extend the DAST-Default-Branch-Deploy template to support ECS

What does this MR do and why?

In order to run DAST on the default branch, we first need to spin up a temporary environment (similar to a review app) and deploy the application. The DAST-Default-Branch-Deploy.gitlab-ci.yml template already supports k8s, and this MR extends it to support ECS as a deployment target.

Related to #228908 (closed)

Screenshots or screen recordings

Sample pipeline: https://gitlab.com/ali-gitlab/golang-app/-/pipelines/569713479

Sample project variables:

MR acceptance checklist

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