Feat/add opa example

[tim775]

No description provided.

[github-actions]

💰 Infracost estimate: monthly cost will increase by $55,065 📈

Project	Previous	New	Diff
infracost/infracost/examples/terraform/plan.json	$0	$55,065	+$55,065

Infracost output

Project: infracost/infracost/examples/terraform/plan.json

+ aws_instance.web_app
  +$55,065

    + Instance usage (Linux/UNIX, on-demand, m5.4xlarge)
      +$41,570

    + root_block_device
    
        + Storage (general purpose SSD, gp2)
          +$371

    + ebs_block_device[0]
    
        + Storage (provisioned IOPS SSD, io1)
          +$9,268
    
        + Provisioned IOPS
          +$3,856

+ aws_lambda_function.hello_world
  Monthly cost depends on usage

    + Requests
      Monthly cost depends on usage
        +$14.83 per 1M requests

    + Duration
      Monthly cost depends on usage
        +$0.0012357988 per GB-seconds

Monthly cost change for infracost/infracost/examples/terraform/plan.json
Amount:  +$55,065 ($0.00 → $55,065)

──────────────────────────────────
Key: ~ changed, + added, - removed

2 cloud resources were detected:
∙ 2 were estimated, 2 include usage-based costs, see https://infracost.io/usage-file

This comment will be updated when the cost estimate changes.

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[alikhajeh1]

We should add the example readme and examples/readme.
Should we merge this after open-policy-agent/opa#4141 is done, or merge it now and change the setup-opa step afterwards?