feat: (callout/go) Adding a sample callout for set_header_based_on_body

[mateustd-ciandt]

Fixes #214

This PR adds a new Go callout service that:

• Conditionally buffers request/response bodies when enabled via config
• Analyzes complete body content and adds informational headers
• Supports format detection (JSON/XML/text) and error/warning pattern matching
• Maintains request state with automatic cleanup to prevent memory leaks
• Includes comprehensive unit tests for all handlers
• The service can be enabled by configuring the "body_buffering" option.