top-level error handling

[edwardfoyle]

Problem

The error handler attached to the yargs commands does not execute if an error is thrown by a sigint handler (or any other process listener). This meant that if a customer hit ctrl+C to stop sandbox (which invokes the sigint handler), then hit ctrl+C again to exit the "do you want to delete the sandbox" prompt, the error thrown by inquirer in the sigint handler would not go through the yargs error handler and instead becomes a top-level unhandled rejection

Issue number, if available:
Fixes #821

Changes

1. Removes all individual command failure handlers and replaces with one top level command failure handler. yargs will execute this failure handler for any command failure
2. Adds error handlers for the unhandledRejection and uncaughtException process events. This ensures that errors thrown outside of yargs are still handled
3. Some small refactors to support the two changes above
4. test additions and updates

Corresponding docs PR, if applicable:

Validation

Tested various failure scenarios locally, updated unit tests, existing tests pass and added additional unit tests

Checklist

• If this PR includes a functional change to the runtime behavior of the code, I have added or updated automated test coverage for this change.
• If this PR requires a change to the Project Architecture README, I have included that update in this PR.
• If this PR requires a docs update, I have linked to that docs PR above.
• If this PR modifies E2E tests, makes changes to resource provisioning, or makes SDK calls, I have run the PR checks with the run-e2e label set.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[changeset-bot]

🦋 Changeset detected

Latest commit: ff16f27

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
@aws-amplify/backend-cli	Patch

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[0618]

LGTM!