Make ECS Review apps work with DAST

What does this MR do and why?

Get the task hostname and artifact it in environment_url.txt so that it can be used by the DAST job in a later stage.

Related to #228908 (closed)

Screenshots or screen recordings

Sample MR with review app, SAST, and DAST: ali-gitlab/golang-app!5 (closed)

Sample project variables:

MR acceptance checklist

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