Add context param in interceptor

**Is your feature request related to a problem? Please describe.**
I want to add opentracing tracking for message delivery. Executing opentracing related code in the interceptor is an elegant way which won't cause a bad influence on my logic code. However, the interceptor has no context parameter, which makes it difficult to pass in the relevant context.

**Describe the solution you'd like**
I want to add context param in ProducerInterceptor's BeforeSend method.
BeforeSend(producer Producer, message *ProducerMessage)
↓
BeforeSend(ctx context.Context, producer Producer, message *ProducerMessage)

Start by locating ProducerInterceptor and its BeforeSend method, then inspect every call site and any related interceptor tests. The issue's requested change is complete when BeforeSend accepts a context.Context and the relevant producer message delivery path passes it through without changing existing interceptor behavior.

Written by the indexing model from the issue text.