feat(docs): add theme-park middleware docs (#3320)

* feat(docs): add theme-park middleware docs

* bump

charts/stable/traefik/Chart.yaml

@@ -22,7 +22,7 @@ sources:
   - https://github.com/traefik/traefik-helm-chart
   - https://traefik.io/
 type: application
-version: 13.1.6
+version: 13.1.7
 annotations:
   truecharts.org/catagories: |
     - network

charts/stable/traefik/docs/theme-park-middleware.md

@@ -0,0 +1,44 @@
+# Theme Park
+
+Theme park is a middleware to inject [supported stylesheets (css)](https://docs.theme-park.dev/theme-options)
+into [supported apps](https://docs.theme-park.dev/themes).
+
+So let's see how to do that.
+
+Note that this will only work on apps you have enabled `ingress`, and only when accessing them via the URL.
+Will NOT work if you access them via `IP:PORT`.
+
+## Creating the middleware on traefik
+
+Edit your existing traefik install (or install fresh if you don't have it installed)
+
+- Scroll down to `theme-park`
+- Click <kbd>Add</kbd>
+- Name: `guactheme` (Any name you want, remember it, you will need it later)
+- App Name: `guacamole` (Replace with the name of the app you want to theme)
+- Theme Name: `plex` (Replace wit the theme you want to apply)
+- Base URL: (Leave the default, unless you plan to use a self hosted theme provider)
+- Click <kbd>Save</kbd>
+
+  ![traefik-theme-fields](img/traefik-theme-fields.png)
+
+> Keep in mind that if you decide to use a self hosted theme provider, it will need to have enabled ingress.
+> Also use the external URL, not the internal, as the client will need to access that theme provider to fetch the
+> stylesheets.
+
+## Applying the theme to the app
+
+Edit your existing _App_, in this example we will use `guacamole-client`.
+
+- Scroll down to `Treafik MIddlewares` (Remember, you need to have `ingress` enabled)
+- Click <kbd>Add</kbd>
+- Name: `guactheme` (Replace with the name you gave to your middleware on the previous step)
+- Click <kbd>Save</kbd>
+
+  ![traefik-theme-app](img/traefik-theme-app.png)
+
+You are ready!
+
+|                        Before                         |                        After                        |
+| :---------------------------------------------------: | :-------------------------------------------------: |
+| ![traefik-theme-before](img/traefik-theme-before.png) | ![traefik-theme-after](img/traefik-theme-after.png) |