Use tfsec instead of DivvyCloud scan in CI

[GaryGSC]

No description provided.

[github-actions]

Terraform Plan:

will create 1 resource:

• local_file - appspec_json

will update 2 resources:

• aws_alb_listener - https
• aws_alb_listener - test_listener

will replace (delete then create) 1 resource:

• aws_ecs_task_definition - task_def

see details

[GaryGSC]

This has some rough edges that need to be resolved upstream.

In this repo, we need to specify working_directory to point the action to the shared Terraform bits so that we get relevant results, but then the SARIF results are relative to that directory (when they need to be relative to the repo's root to play nicely with GHAS).

[GaryGSC]

Refs: #350

[GaryGSC]

#980 helps resolve some of the directory issues involved here.