Improve Pan language support (#3691)

* Add a larger set of sample files for Pan

This is a fairly good cross section of Pan based on code from:
* https://github.com/quattor/template-library-examples
* https://github.com/quattor/template-library-core

* Add Pan language grammar

samples/Pan/osd-fetch.pan

@@ -0,0 +1,26 @@
+unique template site/ceph/osdschemas/osd-fetch;
+
+prefix '/software/components/ceph/clusters/ceph';
+
+variable FETCHED_OSDS = {
+    t = dict();
+    rep = 2;
+    foreach(idx; host; CEPH_NODES) {
+        prof = replace('.data$', '.os', host);
+        d = value(format('%s:/software/components/ceph/localdaemons/osds', prof));
+        t[shorten_fqdn(host)] = dict(
+            'fqdn', host,
+            'osds', d
+        );
+
+        numosd = length(d);
+        if (numosd > rep){
+            rep = numosd;
+        };
+    };
+    all = dict('osdhosts', t, 'maxosd', rep);
+};
+
+'osdhosts' = FETCHED_OSDS['osdhosts'];
+variable CEPH_OSD_DOWN_REPORTERS ?= FETCHED_OSDS['maxosd'] + 2;
+variable CEPH_OSD_DOWN_REPORTS ?=  CEPH_OSD_DOWN_REPORTERS + CEPH_OSD_DOWN_REPORTERS / 4 + 1;