Log SDK version on REST calls

As an IronCore audit log user
I want to know what SDK and version make a request to the IronCore service
- so that SDKs with specific behaviors/defects can be recognized and isolated
- so that I can tell if there are out of date clients making requests for encrypted data

AC:
* [ ] Every REST request to the IronCore service should include a header `X-IronCore-Sdk-Version`. Values of the header should be of the form `ironoxide ..` and should match the current version of the SDK sending the request.
* [ ] This header should be visible at the ironcore service and should be logged to the requests audit trail

This looks like a promising path: https://doc.rust-lang.org/cargo/reference/environment-variables.html

Start by tracing where the Rust SDK constructs REST requests and review Cargo's environment-variable documentation, which the issue identifies as a promising path. The work is done when every request carries an X-IronCore-Sdk-Version header matching the SDK version and that header appears in the service's request audit trail.

Written by the indexing model from the issue text.