Populate configuration in .env instead of config.json

[trivikr]

Is your feature request related to a problem? Please describe.

The credentials are populated in https://github.com/aws-samples/aws-sdk-js-notes-app/blob/main/packages/frontend/src/config.json which is not ignored by git.

It can be mistakenly added to commit when working on frontend.

Describe the solution you'd like

Create .env.example with dummy data, and populate configurations in .env which can be ignored by git.

Describe alternatives you've considered

N/A

Additional context

Docs: https://vitejs.dev/guide/env-and-mode