Enable developers to log request/response

Description

I would like to log all interactions with Slack so that I can see what gets sent across the wire.

What type of issue is this? (place an x in one of the [ ])

• bug
• enhancement (feature request)
• question
• documentation related
• testing related
• discussion

Requirements (place an x in each of the [ ])

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.

Bug Report

Getting the Request information is fairly easy by doing the following:

// Show Received payload
app.use(async ({ next, payload, body, client, context }) => {
    util.prettyJSON(payload, 'RECEIVED (payload): ');
    await next();
});

However, getting the Response information has been more challenging. So far, I am doing the following, which works, but probably isn't the best way:

const logSent = config => {
    util.prettyJSON(config, 'SENT: ')
    return config;
}

// Show sent payload
app.client.axios.interceptors.request.use(logSent, error => Promise.reject(error));
app.use(async ({ next, client }) => {
    if (client.fixed !== true) {
        client.axios.interceptors.request.use(logSent, error => Promise.reject(error));
        client.fixed = true;
    }
    await next();
});

I would prefer to do this at a framework level in one place, rather than in each individual listener. Is there a better way?

Reproducible in:

package version: 2.0.1

node version: v13.12.0

OS version(s): Mac 10.15.3

Steps to reproduce:

1. Send a request to bot
2. Send a response via .say()
3. Send a response via api.client.[]
4. Send a response via listener's client.[]

Expected result:

1. Send a request to bot and log the request
2. Send a response via .say() and log the response
3. Send a response via api.client.[] and log the response
4. Send a response via listener's client.[] and log the response

The issue names app.use middleware and app.client.axios interceptors as current entry points; start by tracing how requests from .say(), api.client.[], and listener client.[] flow through the framework. Done means a framework-level mechanism can log incoming requests and outgoing responses for all four paths, with coverage for those cases.