Implement Secret storage backend as gRPC server

[pkosiec]

Description

Changes proposed in this pull request:

• Add Protocol Buffers schema
• Generate gRPC client + server code from Protocol Buffers
• Implement gRPC server for secret storage backend
  • Support initially just AWS Secrets Manager. Tested also dotenv provider. The vault provider needs to be tested
  • Add tests for the gRPC server with fake secret provider

TODO

• Update Development guide on website: Mention gRPC client and server code generation website#110
• Create PR with dotenv and AWS Secrets Manager for teller repo (Support deleting secrets for AWS Secrets Manager and dotenv providers tellerops/teller#60)

Notes

Lint failing because of timeout. Don't worry about it - The job will be green after review 🙂

Testing

To regenerate the gRPC code, run:

SKIP_DEPS_INSTALLATION=false make gen-grpc-resources

To run example calls against the gRPC service:

1. Create AWS security credentials with SecretsManagerReadWrite policy.

2. Export environment variables:

    export AWS_ACCESS_KEY_ID="{accessKey}"
    export AWS_SECRET_ACCESS_KEY="{secretKey}"

3. Run the server:

   APP_SUPPORTED_PROVIDERS=dotenv,aws_secretsmanager APP_LOGGER_DEV_MODE=true go run ./cmd/secret-storage-backend/main.go

4. Now let's use Go generated gRPC client to to see how the server behaves. Run the example pkg/hub/api/grpc/storage_backend/example_test.go.

   To run it, you can e.g. change the func ExampleNewStorageBackendClient() { to func TestE2EScenario(t *testing.T) { and run it as an usual test.

5. Change the line 12 of this test and run it again:

   provider := "aws_secretsmanager"

Related issue(s)

Resolves #637

[mszostok]

I really enjoyed reviewing your PR, really nice work 👍

[mszostok]

tutti bueno 😄 🚀

[mszostok]

Probably even earlier, as using the dotenvwill be useful in e2e tests, so we will need to add some padding to other task to figure this out or you can create a follow-up task to enable the Secret Store storage "consumption" by Local Hub.

[pkosiec]

Integration tests failed during Capact iunstallation, but the previous run was successful (https://github.com/capactio/capact/actions/runs/1900095690) - and also this PR doesn't change anything related to integration tests, so I'm merging this without retry.