Add support for dotenv

[lewispeel]

I tried to add a .env file to the boilerplate project I got from npx @lightningjs/blits@latest but ran into a few errors. This PR changes the boilerplate code so that .env.* files can be used.

Changes

• Example .env.example file added.
• .gitignore ignores any .env files.
• ecmaVersion in eslintrc.cjs uses 2020.
• Added /// <reference types="vite/client" /> to vite.config.js
• Fix component name in Home.js.

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