fix(oam): kuma inventory target-field bug + add-ping tooling [#343][#435]

kuma-inventory.py printed the junk url field (https://) instead of the
hostname for ping monitors — hid ~100 monitors from FQDN matching.
kuma-add-ping.py: idempotent ping-monitor adds (exists-check by name and
target). Matrix published to Discourse t/309 (canonical, #343).

Detail: https://projects.knownelement.com/issues/343

scripts/kuma-inventory.py

@@ -63,7 +63,8 @@ def main():
             mtype = m.get("type") or "?"
             active = "on" if m.get("active", True) else "PAUSED"
             name = (m.get("name") or "?").replace("\t", " ")
-            target = (m.get("hostname") if m.get("type") == "dns" else None) or m.get("url") or m.get("hostname") or ""
+            # hostname first: ping monitors carry a junk default url ("https://")
+            target = m.get("hostname") or m.get("url") or ""
             target = str(target).replace("\t", " ")
             rows.append((mid, parent, mtype, active, name, target))
         rows.sort(key=lambda r: (r[1] == "-", r[1], r[4].lower()))