Managing large amounts of environment variables

### Command

build, serve, test, e2e

### Description

I am reopening https://github.com/angular/angular-cli/issues/4318.

Essentially we need a way to pass environment variables to the build/serve commands. environments.ts file is not a viable solution as you would need to end up with hundreds of environment.ts files depending on all the permutations per environment.

The solution to https://github.com/angular/angular-cli/issues/4318 also does not address this since you need to know the `define` values when running the command `ng build ....`
Which means you would have to generate the build command same way as generating the `environment.ts` file.

Most enterprise angular applications I have worked on ends up extending the `webpack.config.js` file adding:
```javascript
DefinePlugin({
process: {
env: {
VAR_1: JSON.stringify(process.env.VAR_1),
...
}
}
})
```

This issue has been brought up for years with the Angular repo but i've never seen a resolution so I want to try to make it as clear as possible.
We should support a `dotenv()` style solution where in the code we can use `process.env.VARIABLE`.
In the build machine we can either:
`export VARIABLE=test`
or have a `.env` file to pick it up.

This is supported by pretty much every other framework out there so I'm not sure why it wouldn't be possible or hasn't already been implemented.

If the issue is the angular team doesn't want this behaviour then that is fine but I am looking for a yes/no type answer. If the answer is no the angular team would be able to point to this issue for all future feature requests of this nature.

### Describe the solution you'd like

_No response_

### Describe alternatives you've considered

_No response_

Beginne mit dem vorherigen Issue #4318 und den Einstiegspunkten der build-, serve-, test- und e2e-Befehle. Prüfe den bestehenden Ansatz von environments.ts und das DefinePlugin-Beispiel in webpack.config.js und ermittle anschließend, wie exportierte Variablen oder eine .env-Datei als process.env.VARIABLE bereitgestellt werden sollen. Als erledigt gilt, wenn das unterstützte Verhalten und der Geltungsbereich für diese Befehle definiert sind.

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