feat(@angular-devkit/build-angular): add assets option to server builder

This commits adds the `assets` option to the server builder. This can be useful to copy server specific assets such as config files.

Closes angular#24203

Author: alan-agius4

packages/angular_devkit/build_angular/src/builders/server/schema.json

@@ -4,6 +4,14 @@
   "title": "Universal Target",
   "type": "object",
   "properties": {
+    "assets": {
+      "type": "array",
+      "description": "List of static application assets.",
+      "default": [],
+      "items": {
+        "$ref": "#/definitions/assetPattern"
+      }
+    },
     "main": {
       "type": "string",
       "description": "The name of the main entry-point file."
@@ -207,6 +215,44 @@
   "additionalProperties": false,
   "required": ["outputPath", "main", "tsConfig"],
   "definitions": {
+    "assetPattern": {
+      "oneOf": [
+        {
+          "type": "object",
+          "properties": {
+            "followSymlinks": {
+              "type": "boolean",
+              "default": false,
+              "description": "Allow glob patterns to follow symlink directories. This allows subdirectories of the symlink to be searched."
+            },
+            "glob": {
+              "type": "string",
+              "description": "The pattern to match."
+            },
+            "input": {
+              "type": "string",
+              "description": "The input directory path in which to apply 'glob'. Defaults to the project root."
+            },
+            "ignore": {
+              "description": "An array of globs to ignore.",
+              "type": "array",
+              "items": {
+                "type": "string"
+              }
+            },
+            "output": {
+              "type": "string",
+              "description": "Absolute path within the output."
+            }
+          },
+          "additionalProperties": false,
+          "required": ["glob", "input", "output"]
+        },
+        {
+          "type": "string"
+        }
+      ]
+    },
     "fileReplacement": {
       "oneOf": [
         {