WIP :Use key-value-storage/policy-engine crates to make Trustee stateless

[Xynnn007]

Summary

This a second part of #1093. Including the following changes

• Use key-value-storage to replace RVPS's storage backend
• A Refactoring upon policy-engine to allow supporting extensions
• Use policy-engine to replace AS's policy engine implementation
• Use policy-engine to replace KBS's policy engine implementation. Move the KBS policy unit tests to policy-engine crate.
• Fix integration-tests and trustee-cli code to follow the mentioned underlying crates.
• Update the README.mds.

Config Changes

Hi @lmilleri @bpradipt , the main changes of the user interface are two

1. AS/KBS Config format is included in the commit ; RVPS Config format is included in the commit.

For RVPS, config format does not change.

For AS, config format would be changed to

{
        "work_dir": "/opt/confidential-containers/attestation-service",
        "rvps_config": {
          "type": "GrpcRemote",
          "address": "http://127.0.0.1:50003"
        },
        "attestation_token_broker": {
          "type": "Ear",
          "policy_engine": {
            "storage": {
              "type": "LocalFs",
              "dir_path": "/opt/confidential-containers/attestation-service/policies"
            }
          }
        },
        "attestation_token_config": {
          "duration_min": 5
        }
    }

For KBS, config format would be changed to

[http_server]
sockets = ["0.0.0.0:8080"]
insecure_http = true
worker_count = 4

[admin]
insecure_api = true
auth_public_key = "/etc/auth-secret/kbs.pem"

[attestation_token]
insecure_key = true

[attestation_service]
type = "coco_as_grpc"
as_addr = "http://127.0.0.1:50004"

[[plugins]]
name = "resource"
backend = "kvstorage"
type = "LocalFs"
dir_path = "/opt/confidential-containers/kbs/repository"

[policy_engine.storage]
type = "LocalFs"
dir_path = "/opt/confidential-containers/opa"

And for KBS, the resource policy will not be a directly specified file. Instead, it will be the value that key resource-policy points to in the backend kv-storage. What does this mean? It means if we use LocalFs like in this example, the policy file should be the file resource-policy.rego under /opt/confidential-containers/opa path, s.t. file /opt/confidential-containers/opa/resource-policy.rego.

2. The format of LocalJson.

Before this PR, the reference values in the LocalJson backend file looks like

[
    {
        "expiration": "1970-01-01T00:00:00Z",
        "name": "artifact1",
        "version": "1.0.0",
        "value": "abcd"
    },
    {
        "expiration": "1970-01-01T00:00:00Z",
        "name": "artifact2",
        "version": "2.0.0",
        "value": "efgh"
    }
]

But after this PR, it would like

{
    "artifact1": "ewogICAgImV4cGlyYXRpb24iOiAiMTk3MC0wMS0wMVQwMDowMDowMFoiLAogICAgIm5hbWUiOiAiYXJ0aWZhY3QxIiwKICAgICJ2ZXJzaW9uIjogIjEuMC4wIiwKICAgICJ2YWx1ZSI6ICJhYmNkIgp9",
    ...
}

where ewo.. is base64-encoding of original

{
      "expiration": "1970-01-01T00:00:00Z",
      "name": "artifact1",
      "version": "1.0.0",
      "value": "abcd"
}

and the key is the name field.

What's More

Hi @mkulke ,

The current PR still has over 1000 lines because each subcomponent (KBS/AS/RVPS) needs to update the global configuration README after replacing relevant parts. I want to be able to include all the README changes in a single PR to make it easier for TrusteeOperator folks a better view.

Not sure if it is acceptable - or do you have better idea to re-organize the PR for reviewing?