Debugging mode

[erunion]

Because a lot of the work that api does behind the scenes can be a bit magical it'd be nice if there was some sort of debugging mode that you could enable that would log out the HAR that we use in the backend with fetch-har.

const sdk = require('@api/petstore');

// leaf handling
sdk.debug();
sdk.operation().then(...)

const sdk = require('@api/petstore');

sdk.debug().operation().then(...)

Perhaps the chained mode should only apply the debug mode to the operation it's attached to.

[erunion]

moving this to #789