Map idempotency headers to worker-executor invocation keys

[vigoo]

The headers mentioned in https://github.com/golemcloud/golem/issues/323 could also be supported on the "server side", when providing a HTTP API on top of Golem workers.

Worker executors already support this with the invocation key.

[justcoon]

i think that this issue is already implemented: worker_binding_resolver cc: @afsalthaj, @vigoo