add metrics docs

console/metrics.adoc

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+include::../partials/attributes.adoc[]
+[id="metrics"] 
+= Flow metrics
+
+The following metrics are available to a Prometheus instance when you enable the flow collector using `skupper init --enable-flow-collector`
+
+flows_total:: For tcp protocol this is the total number of connections. 
+For http or http2 protocol this is the total number of distinct requests made.
+
+octets_total:: The total number of bytes processed by the router.
+
+active_flows:: The number of flows currently active including open tcp connections and _in flight_ http requests.
+
+address_last_time_seconds:: The time since a flow was last observed in seconds.
+
+flow_latency_microseconds:: The latency in microseconds, as observed by the first and last router involved in the flow.
+
+http_requests_method_total:: Total number of http requests grouped by method.
++
+Additional label: The http method, for example, `GET`, `HEAD`, `POST`.
+
+http_requests_result_total:: Total number of http requests by response code.
++
+Additional label: The http response code, for example `200`, `403`, `503`.
+
+activeLinks:: The total number of links between sites.
+
+activeRouters:: The total number of routers.
+
+activeSites:: The total number of sites.
+
+
+The following labels are common to these metrics allowing you to filter and categorize the data:
+
+address:: The address relating to the metric.
+Typically, this is the service name.
+
+sourceSite:: The site where the flow originated for the metric. 
+This string is a combination of the site name and the site ID.
+
+destSite:: The site where the flow terminated for the metric. 
+This string is a combination of the site name and the site ID.
+
+direction:: The direction of flow.
+For traffic sent from a client to server the value is `incoming`.
+For traffic sent from a client to server the value is `outgoing`.
+
+protocol:: The protocol used by the flow, `tcp`, `http`, or `http2`.
+
+sourceProcess:: The name of the process originating the flow.
+
+destProcess:: The name of the process receiving the flow.