Add metrics per_host documentation to caddy website. (#455)

* Update metrics.md

* Added per_host documentation to options.md

* Updated list of all options to include per_host metrics option

* Update metrics code block to reflect change

Per mohammed90

The metrics config is now moved outside of the servers option.

* Fixed indentation issue options.md

* Update src/docs/markdown/caddyfile/options.md

Co-authored-by: Mohammed Al Sahaf <mohammed@caffeinatedwonders.com>

* Update src/docs/markdown/metrics.md

Co-authored-by: Mohammed Al Sahaf <mohammed@caffeinatedwonders.com>

* Update src/docs/markdown/caddyfile/options.md

---------

Co-authored-by: Mohammed Al Sahaf <mohammed@caffeinatedwonders.com>
Co-authored-by: Francis Lavoie <lavofr@gmail.com>

src/docs/markdown/caddyfile/options.md

@@ -76,7 +76,9 @@ Possible options are (click on each option to jump to its documentation):
 	}
 	grace_period   <duration>
 	shutdown_delay <duration>
-	metrics
+	metrics {
+		per_host
+	}
 
 	# TLS Options
 	auto_https off|disable_redirects|ignore_loaded_certs|disable_certs
@@ -969,6 +971,15 @@ Enables Prometheus metrics collection; necessary before scraping metrics. Note t
 }
 ```
 
+You can add the `per_host` option to label metrics with the host name of the metric.
+
+```caddy
+{
+	metrics {
+		per_host
+	}
+}
+```
 
 ##### `trace`
 

src/docs/markdown/metrics.md

@@ -17,14 +17,22 @@ If using a Caddyfile, enable metrics [in global options](/docs/caddyfile/options
 
 ```caddy
 {
-    servers {
+	metrics
-        metrics
-    }
 }
 ```
 
 If using JSON, add `"metrics": {}` to your [`apps > http > servers` configuration](/docs/json/apps/http/servers/).
 
+To add per-host metrics you can insert the `per_host` option. Host specific metrics will now have a Host tag.
+
+```caddy
+{
+	metrics {
+		per_host
+	}
+}
+```
+
 ## Prometheus
 
 [Prometheus](https://prometheus.io) is a monitoring platform that collects