feat(config): add yaml config file support

[konippi]

Summary

Changes

Please provide a summary of what's being changed

Add support for loading configuration from YAML files, allowing users to manage complex configurations more easily. CLI arguments take precedence over file configuration for maximum flexibility.

User experience

Please share what the user experience looks like before and after this change

Before

# Long command line with many arguments
mcp-proxy-for-aws https://example.com/mcp \
  --service my-service \
  --profile production \
  --region us-east-1 \
  --read-only \
  --log-level DEBUG \
  --retries 3 \
  --timeout 200

After

# Simple command with config file
mcp-proxy-for-aws --config config.yaml

Checklist

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• I have reviewed the contributing guidelines
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented

Is this a breaking change? (Y/N)

• Yes
• No

Please add details about how this change was tested.

• Did integration tests succeed?
• If the feature is a new use case, is it necessary to add a new integration test case?

Acknowledgment

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[wzxxing]

Hi @konippi, thanks a lot for your PR.

Our project was only recently released so we did not have a mechanism for RFCs. This is a new feature and ideally we would like you to open a issue in the project. I will add this to the contributing guideline soon.

We do have plan to introduce a config feature, but it is not for local config, but the server-side config. And we are thinking of using --config parameter as a "append` argument (can be specified many times). e.g.

mcp-proxy-for-aws --config AWS_REGION=$AWS_REGION \
    --config readonly=true \
    --config timeout=30s
    <endpoint>

The config will be added to the JSON RPC message to send to the remote server. The feature is currently under development so we cannot merge this PR for now.

However, we do think having a config makes sense. We need to figure out a default location of this config such as in $XDG_CONFIG_HOME/mcp-proxy-for-aws.yaml or in ~/.aws/mcp-proxy-for-aws.yaml. It is also possible that the config can be in a aws profile because we have a --profile argument.

I will create a issue for this so that you can track the progress.

[konippi]

Thank you for explaining that to me. I'll close this PR now.