OpenTracing / Context propagation support

未指定文件或测试；请先查看 Ruby SDK 的 workflow 和 activity 配置，以及 Temporal header 的处理方式。该 issue 目前还未准备好实施：workflow 配置接口仍未完成，而完成这项工作需要就自动上下文传播达成一致的设计，并需要用于扩展现有上下文的 workflow 和 activity 方法。

As suggested by @jeffschoner-stripe and @drewhoskins-stripe, I am creating a github issue to discuss the topic of context propagation for the Ruby SDK.

Tracing Proposal

Why

Distributed applications are more difficult to measure and debug due
to the distributed nature of their processing. One cannot simply
attach to the running process with a debugger and capture state
since that state may be spread across multiple processes or systems.
Temporal, by its nature, is distributed. Any application written using
Temporal will also be distributed. In order to trace through the
behavior of the business logic implemented as workflow(s) and
activit(ies) we should provide support for OpenTracing and other
related tracing mechanisms.

The Java, Go, and Typescript SDKs all support OpenTracing today via
context propagation. The Ruby SDK can support Tracing today without
any changes merely by allowing the programmer to pass the Tracing
context as an argument to every workflow and activity. This is sloppy
and error prone, so we should mimic the facilities exposed by the
aforementioned SDKs and allow the context to propagate automatically
using the Temporal headers.

What

This defines the interface for passing in OpenTracing contexts to
the Temporal system. Upon configuration, the propagation of this
information should be automatic and transparent to the programmer.
Aside from initial configuration, methods should be exposed on
the workflow and activity that allow for adding to the existing
(if any) context.

Workflow Configuration

Will fill this out in next edit... thinking about it.