Add configuration option to disable inlined CSS in SSR HTML

When inlining CSS, Angular Universal needs to extract critical styles.
This seems to take up a significant chunk of processing time.

However, loading may appear less smooth when this feature is disabled.

Added to the configuration to make it easier to A/B test this without a full re-build.

src/config/universal-config.interface.ts

@@ -4,4 +4,13 @@ export interface UniversalConfig extends Config {
   preboot: boolean;
   async: boolean;
   time: boolean;
+
+  /**
+   * Whether to inline "critical" styles into the server-side rendered HTML.
+   *
+   * Determining which styles are critical is a relatively expensive operation;
+   * this option can be disabled to boost server performance at the expense of
+   * loading smoothness.
+   */
+  inlineCriticalCss?;
 }