Install/run Amplify as a local package

(no list is shown, pressing space does nothing)

```
$ npx amplify pull
```

### Use cases

* ~~Install amplify without sudo~~ (edit: this can be accomplished by [setting a custom NPM prefix](https://docs.npmjs.com/resolving-eacces-permissions-errors-when-installing-packages-globally/#manually-change-npms-default-directory))
* Lock my version of the Amplify CLI with my project's `package.json` file
* Upgrade the Amplify CLI along with the rest of my project's dependencies
* Be notified of security vulnerabilities found in the Amplify CLI by `npm audit`
* Fix security vulnerabilities found in the Amplify CLI by running `npm audit fix`

### Related issues, documentation, etc

#4491 (2020, closed due to inactivity)
#4485 (2020, closed due to inactivity)
#839 (2019, closed due to inactivity)

PR #3857 (closed due to inactivity)

For more about npx, iincluding use cases, see the _npx launch blog post_ (2017): https://blog.npmjs.org/post/162869356040/introducing-npx-an-npm-package-runner

### Describe the solution you'd like

See above

### Describe alternatives you've considered

I've considered installing amplify globally. It would have to be manually updated, since my package manager would not be aware of it.

I've considered running a dockerized Amplify CLI. This would provide secure and repeatable builds but it's also more work to set up and troubleshoot.

Edit: It's possible to install Amplify globally without sudo by setting a custom npm prefix. This mitigates some of my security concerns and allows the use of `npx`.

### Additional context

* _The problem with npm install --global_ (2017): https://ericlathrop.com/2017/05/the-problem-with-npm-install-global/
* _Avoid global npm installs for projects_ (2015): http://www.gjermundbjaanes.com/avoid-global-npm-installs-for-projects/

### Is this something that you'd be interested in working on?