improve docs, add version script

docs/content/advanced/config/optional-config.md

@@ -3,3 +3,9 @@ title: Optional Configuration
 ---
 
 TODO
+
+| Env        | Default   | Example     | Description                    |
+| ---------- | --------- | ----------- | ------------------------------ |
+| `PORT`     | `51821`   | `6789`      | TCP port for Web UI.           |
+| `HOST`     | `0.0.0.0` | `localhost` | IP address web UI binds to.    |
+| `INSECURE` | `false`   | `true`      | If access over http is allowed |

docs/content/advanced/metrics/prometheus.md

@@ -0,0 +1,7 @@
+---
+title: Prometheus
+---
+
+TODO
+
+<!-- TOOD: add to docs: Grafana dashboard [21733](https://grafana.com/grafana/dashboards/21733-wireguard/) -->

docs/content/advanced/migrate/index.md

@@ -0,0 +1,7 @@
+---
+title: Migrate
+---
+
+If you want to migrate from an older version of `wg-easy` to the new version, you can find the migration guides listed below.
+
+- [Migrate from v14 to v15](./from-14-to-15.md) : This guide should also work for any version before `v14`.