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

该请求针对生产配置中的 ng build 预算，并提议使用 asset:jpg、asset:svg 和 asset:png 子类型；未指定源文件或测试。首先追踪 ng build 使用的现有预算处理逻辑，然后验证超出大小限制的资源是否会针对每个子类型触发已配置的警告和错误阈值。

由索引模型根据 Issue 内容生成。