Documentation Revamp

Co-authored-by: jbdoumenjou <jb.doumenjou@gmail.com>

docs/content/middlewares/errorpages.md

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+# ErrorPage
+
+It Has Never Been Easier to Say That Something Went Wrong
+{: .subtitle }
+
+![ErrorPages](../assets/img/middleware/errorpages.png)
+
+The ErrorPage middleware returns a custom page in lieu of the default, according to configured ranges of HTTP Status codes.
+
+!!! important
+    The error page itself is _not_ hosted by Traefik.
+
+## Configuration Examples
+
+??? example "File -- Custom Error Page for 5XX"
+
+    ```toml
+    [Routers]
+      [Routers.router1]
+        Service = "my-service"
+        Rule = Host(`my-domain`)
+
+    [Middlewares]
+      [Middlewares.5XX-errors.Errors]
+        status = ["500-599"]
+        service = "error-handler-service"
+        query = "/error.html"
+                
+    [Services]
+      # ... definition of error-handler-service and my-service
+    ```
+
+??? example "Docker -- Dynamic Custom Error Page for 5XX Status Code"
+
+    ```yaml
+    a-container:
+      image: a-container-image 
+        labels:
+          - "traefik.middlewares.test-errorpage.errors.status=500-599",
+          - "traefik.middlewares.test-errorpage.errors.service=serviceError",
+          - "traefik.middlewares.test-errorpage.errors.query=/{status}.html",
+            		
+    ```
+    
+    !!! note 
+        In this example, the error page URL is based on the status code (`query=/{status}.html)`.
+
+## Configuration Options
+
+### status
+
+The `status` that will trigger the error page.
+
+The status code ranges are inclusive (`500-599` will trigger with every code between `500` and `599`, `500` and `599` included).
+ 
+!!! Note
+
+    You can define either a status code like `500` or ranges with a syntax like `500-599`.
+
+### service
+
+The service that will serve the new requested error page.
+
+### query
+
+The URL for the error page (hosted by `service`). You can use `{status}` in the query, that will be replaced by the received status code.