How to cache ssr entry resource?

## **BEFORE YOU SUBMIT** please read the following:

* [ ] **I'm submitting a bug report**
* [x] **I'm submitting a feature request**
* [ ] **I'm submitting a support request**

**webpack version:**
4.26

**sw-precache-webpack-plugin version**:
0.11.5

**Please tell us about your environment:**
Windows 10

**Browser:** [Phantom XX | Chrome XX | Firefox XX | IE XX | Safari XX | Other XX]
chromw v69
**Current behavior:**
Because my entry index page is rendered via SSR and is not packaged and generated.
All I want to cache is the SSR generated files, but I can't solve it very well in the configuration.

**Expected/desired behavior:**
Cache pages after SSR

*If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem along with your:*

* **Webpack configuration:**

* **Generated service worker (not minified):**