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

このリクエストは本番構成の ng build バジェットを対象とし、asset:jpg、asset:svg、asset:png のサブタイプを提案しています。ソースファイルやテストは特定されていません。まず ng build で使用されている既存のバジェット処理を追跡し、次にサイズ超過したアセットが各サブタイプに設定された警告しきい値とエラーしきい値をトリガーすることを確認してください。

索引モデルが issue の本文から書いたものです。