Easy proxy config with defaults or inline

[tlong-dev]

Bug Report or Feature Request

• bug report -> please search issues before submitting
• feature request

Versions.

@angular/cli: 1.0.2
node: 7.9.0
os: darwin x64
@angular/animations: 4.1.0
@angular/common: 4.1.0
@angular/compiler: 4.1.0
@angular/core: 4.1.0
@angular/forms: 4.1.0
@angular/http: 4.1.0
@angular/platform-browser: 4.1.0
@angular/platform-browser-dynamic: 4.1.0
@angular/router: 4.1.0
@angular/cli: 1.0.2
@angular/compiler-cli: 4.1.0

Desired functionality.

Level 1
Allow us to specify --proxy-conf command line flag through .angular-cli.json defaults mechanism.

Level 2
Allow inlining of proxy config into .angular-cli.json to reduce the amount of files in the root.

[filipesilva]

I think the first bit is a useful setting for projects that always need to be ran with that proxy. I'd prefer not to inline it though, since it can also be a .js file and it could massively complicate the CLI json file schema.

[ayvazj]

I submitted a PR for this HTH #6493