More Control over Error Logging

Hello, I started using `@google-cloud/functions-framework` and noticed that it is not much compatible with [structured logging](https://cloud.google.com/logging/docs/structured-logging).

Especially, when I use [the CloudEventFunction style](https://github.com/GoogleCloudPlatform/functions-framework-nodejs/blob/db922c08687e7eec124ff0d696e0e60d6bf41df8/src/function_registry.ts#L91) which seems to be the [recommended way when integrating with Cloud Pub/Sub](https://cloud.google.com/functions/docs/tutorials/pubsub), the function must throw in order to mark the request as failed (i.e. [respond with 500](https://github.com/GoogleCloudPlatform/functions-framework-nodejs/blob/db922c08687e7eec124ff0d696e0e60d6bf41df8/src/logger.ts#L51)).

In that case, the default (and inevitable) error logging isn't quite nice. First, error is logged twice 😨 ([1](https://github.com/GoogleCloudPlatform/functions-framework-nodejs/blob/db922c08687e7eec124ff0d696e0e60d6bf41df8/src/function_wrappers.ts#L51), [2](https://github.com/GoogleCloudPlatform/functions-framework-nodejs/blob/db922c08687e7eec124ff0d696e0e60d6bf41df8/src/logger.ts#L40)). Second, neither log is not structured, resulting in the error log being split into multiple entries.


I would like to get more control over how errors are logged. Or, maybe as another solution, a method for marking the request as failed without throwing will satisfy my use case.

Thanks!