Include a custom HTTP LRA version header on REST calls made by our implementation

Our implementation of the LRA specification exposes REST endpoints whose semantics may change over time. As the LRA spec evolves users will need a guarantee that the endpoints behave consistently.

To avoid introducing breaking changes I propose that we version REST API calls made by the implementation using a version header, something like:

OpenStack-API-Version: narayana LRA 5.10.5.Final

or

OpenStack-API-Version: narayana LRA 5.10.5.Final https://<the location of our OpenAPI document>

I went for the OpenStack guideline since it was the only standard I could find for custom headers.

A reason it is narayana specific is that our API offers more than the spec requires.