Support OpenTracing 2.0 to get tracing and metrics capabilities

## Why you need it?

Integrate OpenTracing 2.0 API to make Seata support tracing and metrics.

## How it could be?

Modify seata‘s protocol to support context passing, and access OpenTracing 2.0 API .

## Other related information

#714 , Except OpenTracing 2.0, we also need support SkyWalking .

Start by reading issue #714 and the protocol requirements described here, then determine the Seata entry points affected by context passing and the OpenTracing 2.0 API. Done means Seata supports the required protocol changes and provides tracing and metrics capabilities through the requested API, with the related SkyWalking scope resolved.

Written by the indexing model from the issue text.