add support for Sagan (#14070)

* add sagan instance fetch function

* add sagan discovery

* add sagan poller

* add sagan graphs

* add graph sources

* add sagan to apps page

* remove alert

* more app graph work

* polling fix

* re-order keys and add alert key

* correct field key usage

* add alert and fix a missing unit

* more unit fixes

* add alert status

* add alert rules for sagan

* fix a missing : after S while I am here in the json stat tool helper... also add tests

* now add the tests

* add docs

* point php-cs-fixer at two files

* remove-unneeded sagan instance fetch function

* convert to use app_data

* style fix

* apply bennet-esyoil's suggestions here as well

* update for the new app model

* convert poller to the new method

* convert the sagan device app page

* convert sagan

* doc cleanup

includes/html/pages/apps.inc.php

@@ -388,6 +388,24 @@ $graphs['chronyd'] = [
     'frequency',
     'root',
 ];
+$graphs['sagan'] = [
+    'after',
+    'bytes_ignored',
+    'bytes',
+    'drop_percent',
+    'drop',
+    'eps',
+    'f_drop_percent',
+    'f_dropped',
+    'f_total',
+    'ignore',
+    'match',
+    'max_bytes_log_line',
+    'threshold',
+    'total',
+    'uptime',
+    'alert',
+];
 
 echo '<div class="panel panel-default">';
 echo '<div class="panel-heading">';