Add Go AWS gateway parsing foundation (#107)

* Add Go AWS gateway parsing foundation

- Adds a normalized AWS request context with request ids, region/account defaults, credential-scope parsing, and service/action detection across host, path, query, and target metadata.

- Adds dependency-free AWS Query, JSON RPC, and S3 REST route parsers for future native service handlers.

- Covers representative S3, SQS, IAM, STS, and JSON RPC requests in Go unit tests.

* Fix S3 multipart upload action detection

Author: ctate