Add CLI tool to generate .example.env

[arashi-dev]

It would be useful if we have an official CLI tool for T3 to generate the .example.env file for us based on the env.ts schema, which let's us have a ready boilerplate for large env schema and easily set required values while seeing the definitions in the same place, and also a sync standard documentation (.example.env) for team members that do not know about t3-env.

Features that can be included:

• Generate a .env file with default name example but can be overridden from cli arguments
• Add comments for definitions (type, default values, enums/unions options, min, max, etc.)
• [more advanced] Add a CLI Form for more smooth data entering using inputs based on their types

I wanted to code it as a 3th party tool but it would be better if it becomes official (I can contribute though)

[arashi-dev]

A 2nd Idea is to build a more standard library for generation that generates .env files based standard-schema, (publishes 2 packages: A CLI and a library for programmatic usecase) then we can add this library to the T3 CLI for more smooth usage!