Return invocation ID from context

[sagikazarmark]

I'd like to use it as idempotency key when calling other services.

Currently, the only way to get it is from headers, although I think it's available in the inner context somewhere.

I wanted to raise an issue first before opening a PR though, because I'm not sure this is a good idea.

Another piece of information: from what I can tell, other SDKs expose the invocation ID directly, but I couldn't find a way to get it when using the Rust SDK.

[slinkydeveloper]

Hi @sagikazarmark thanks for the feedback, feel free to open a PR to add it to Context impl

[sagikazarmark]

PR opened