API: System endpoint, more health graphs (#8730)

* API: System endpoint, more health graphs

* Add new line api_functions

* Get count of relationships

Using eloquent

* Add new lines in Models

doc/API/System.md

@@ -0,0 +1,37 @@
+source: API/System.md
+
+### `system`
+
+Display Librenms instance information.
+
+Route: `/api/v0/system`
+
+Input:
+
+-
+
+Example:
+```curl
+curl -H 'X-Auth-Token: YOURAPITOKENHERE' https://librenms.org/api/v0/system
+```
+
+Output:
+```json
+{
+    "status": "ok",
+    "system": [
+        {
+            "local_ver": "1.37-234-g19103ee",
+            "local_sha": "19103ee36f68f009272c15be22e5a7e10a8b0b85",
+            "local_date": "1526480966",
+            "local_branch": "master",
+            "db_schema": 249,
+            "php_ver": "7.2.2",
+            "mysql_ver": "5.5.56-MariaDB",
+            "rrdtool_ver": "1.4.8",
+            "netsnmp_ver": "NET-SNMP 5.7.2"
+        }
+    ],
+    "count": 1
+}
+```

doc/API/index.md

@@ -66,3 +66,4 @@ Output from the API currently is via two output types.
 - [ARP](ARP.md)
 - [Services](Services.md)
 - [Logs](Logs.md)
+- [System](System.md)