Proposal: Asset Budgets potentially w/ subtypes

### Bug Report or Feature Request (mark with an `x`)
```
- [ ] bug report -> please search issues before submitting
- [x] feature request
```

### Command (mark with an `x`)
```
- [ ] new
- [x] build
- [ ] serve
- [ ] test
- [ ] e2e
- [ ] generate
- [ ] add
- [ ] update
- [ ] lint
- [ ] xi18n
- [ ] run
- [ ] config
- [ ] help
- [ ] version
- [ ] doc
```

### Versions
Mac High Sierra

```
MacBook-Pro:~ damien$ node --version
v8.9.4
```
```
MacBook-Pro:~ damien$ npm --version
5.6.0
```

```
MacBook-Pro:daffodil damien$ ng --version

_ _ ____ _ ___
/ \ _ __ __ _ _ _| | __ _ _ __ / ___| | |_ _|
/ △ \ | '_ \ / _` | | | | |/ _` | '__| | | | | | |
/ ___ \| | | | (_| | |_| | | (_| | | | |___| |___ | |
/_/ \_\_| |_|\__, |\__,_|_|\__,_|_| \____|_____|___|
|___/

Angular CLI: 7.1.0
Node: 8.9.4
OS: darwin x64
Angular: 7.1.1
... animations, common, compiler, compiler-cli, core, forms
... http, language-service, platform-browser
... platform-browser-dynamic, router, service-worker

Package Version
------------------------------------------------------------
@angular-devkit/architect 0.10.7
@angular-devkit/build-angular 0.10.7
@angular-devkit/build-ng-packagr 0.10.7
@angular-devkit/build-optimizer 0.10.7
@angular-devkit/build-webpack 0.10.7
@angular-devkit/core 7.1.0
@angular-devkit/schematics 7.1.0
@angular/cdk 7.1.0
@angular/cli 7.1.0
@angular/pwa 0.11.3
@ngtools/json-schema 1.1.0
@ngtools/webpack 7.0.7
@schematics/angular 7.1.0
@schematics/update 0.11.0
ng-packagr 4.4.0
rxjs 6.3.3
typescript 3.1.6
webpack 4.19.1
```

### Repro steps
1. Have bundle with 2mb budget
2. Desire a budget that says all image assets are under 1mb.
3. Create an asset that is 1.5mb
4. Be unable to know that the asset outside of budget range as the "any" budget type will catch the bundle.

### The log given by the failure
N/A

### Desired functionality
I would like to set a budget **specifically** for image assets in my `ng build`. Ideally, I can configure this per image type (as each image type has different compressability.

e.g
```
{
...
"configurations": {
"production": {
...
budgets: [
{"type": "asset:jpg", "maximumWarning": "150kb", "maximumError": "300kb"},
{"type": "asset:svg", "maximumWarning": "15kb", "maximumError": "30kb"},
{"type": "asset:png", "maximumWarning": "150kb", "maximumError": "300kb"},
]
}
}
}
```

The use case here is automation around enforcing filesize requirements for assets to prevent absurd image sizes from being included. While `"type": "any"` meets this requirement, there are niches of asset types that should have stricter requirements (e.g. `svg`).

### Mention any other details that might be useful
I'm trying to create budgets for the assets we use on the `Daffodil` project:
https://github.com/graycoreio/daffodil

Specifically, the PR in question:
https://github.com/graycoreio/daffodil/pull/171

La demande cible les budgets de ng build dans la configuration de production et propose les sous-types asset:jpg, asset:svg et asset:png ; aucun fichier source ni test n’est identifié. Commencez par retracer la gestion existante des budgets utilisée par ng build, puis vérifiez que les assets dépassant la taille autorisée déclenchent les seuils d’avertissement et d’erreur configurés pour chaque sous-type.

Rédigé par le modèle d'indexation à partir du texte de l'issue.