Clean up x-proton headers in Rest API spec and Proton SDKs

[chenziliang]

Describe what enhancement you'd like to have
We have some leftovers in the REST API spec regarding x-proton- header and we probably used x-proton- header in (Java) SDKs. Fix them to use x-timeplu- header.

https://github.com/timeplus-io/proton/tree/develop/spec/rest-api
https://github.com/timeplus-io/proton-java-driver