Documentation Revamp

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

docs/content/middlewares/addprefix.md

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+# Add Prefix
+
+Prefixing the Path 
+{: .subtitle }
+
+![AddPrefix](../assets/img/middleware/addprefix.png) 
+
+The AddPrefix middleware updates the URL Path of the request before forwarding it.
+
+## Configuration Examples
+
+??? example "File -- Prefixing with /foo"
+
+    ```toml
+    [Middlewares]
+      [Middlewares.add-foo.AddPrefix]
+         prefix = "/foo"
+    ```
+
+??? example "Docker -- Prefixing with /bar"
+
+    ```yaml
+    a-container:
+      image: a-container-image 
+        labels:
+          - "traefik.middlewares.add-bar.addprefix.prefix=/bar"
+    ```
+
+## Configuration Options
+
+### prefix
+
+`prefix` is the string to add before the current path in the requested URL. It should include the leading slash (`/`).