Implements http.send builtin

[MatMaul]

Spec

Implemented:

• url
• method
• body
• raw_body
• headers
• enable_redirect
• force_json_decode
• force_yaml_decode
• timeout
• raise_error
• max_retry_attempts

The rest of the parameters are about TLS and cache behavior control and are not implemented.

serde_yaml has been replaced by serde_yml since the former is unmaintained.

[Lupus]

Would be awesome to be able to provide custom implementation for actual HTTP client when initializing the policy evaluator or probably runtime. As WASM OPA backend does not support custom built-ins unlike Golang interpreted version, custom HTTP client could be used to call back into the host application from the policy to perform some actions which are not convenient to express via OPA (do some DB request, or actually perform HTTP request or a set of HTTP requests which are a single logical operation from policy perspective).

[MatMaul]

@Lupus I think what you want to do is already possible with this PR: you can provide your own implementation of send_http by customizing the context before instantiating the engine.

It can be the use of another HTTP lib than reqwest, or something that would intercept specific calls and forward to the default reqwest impl if not intercepted.

[Lupus]

@MatMaul could you please provide a sign-off according to this repository's contribution guidelines?