[Producer] Add context to ProducerInterceptor

[treuherz]

Fixes #443

Motivation

The ProducerInterceptor does not take a context.Context. This makes it difficult to write useful interceptors that can integrate with common tracing SDKs like OpenTelemetry. These SDKs typically follow the convention of using a Context to propagate metadata vertically through a call stack.

If an interceptor knows that the pre-Send method can put metadata (such as trace IDs or logging values) in a context.Context, which the post-Send method will be able to pull out, then it does not have to do its own potentially-costly state management.

For an example of a another library using a similar convention, see pgx, the Postgres go driver

Modifications

This change adds a context.Context argument to the ProducerInterceptor interface, and passes it between the pre- and post-Send interceptor methods.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• Unit tests that rely on values in the interceptor context.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): no
• The public API: yes, adding parameters to Interceptor interface
• The schema: no
• The default values of configurations: no
• The wire protocol: no

Documentation

• Does this pull request introduce a new feature? sort of
• If yes, how is the feature documented? go docs