refactor(@angular/cli): add peerDependenciesMeta to package manifest interface

Adds the peerDependenciesMeta property to the PackageManifest interface in the package managers utility to better represent package metadata.

Author: clydin

packages/angular/cli/src/package-managers/package-metadata.ts

@@ -89,6 +89,9 @@ export interface PackageManifest {
   /** A mapping of peer dependencies. */
   peerDependencies?: Record<string, string>;
 
+  /** A mapping of peer dependency metadata */
+  peerDependenciesMeta?: Record<string, { optional?: boolean }>;
+
   /** A mapping of development dependencies. */
   devDependencies?: Record<string, string>;