Embed vcpkg configuration in manifest

[vicroms]

Allows specifying vcpkg configuration in manifest files.

The configuration is passed via a vcpkg-configuration object in the manifest file.
Having a vcpkg-configuration block in vcpkg.json while also having a vcpkg-configuration.json file is not allowed.

As a drive-by format-manifest has been changed to allow the configuration blocks.

Example:

{
  "vcpkg-configuration": {
    "registries": [
      {
        "kind": "git",
        "baseline": "dacf4de488094a384ca2c202b923ccc097956e0c",
        "repository": "https://github.com/northwindtraders/vcpkg-registry",
        "packages": [ "beicode", "beison" ]
      }
    ]
  },
  "name": "test",
  "version": "1.0.0",
  "dependencies": [ "beison", "zlib" ]
}

[strega-nil-ms]

(I understand that putting this under a $ makes it so you don't have to modify manifest parsing code, but it shouldn't be too much work - two lines changed, I think)

[BillyONeal]

nit nit nit nit

[BillyONeal]

In the 1PM meeting we resolved this as "no x-" and we'll warn about it.

[vicroms]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).