jenkins: Add CronJob for updatecheck

`updatecheck` is a little utility I wrote that queries Fedora Bodhi for
updates and sends an HTTP request when one is found.  I am specifically
going to use it to trigger rebuilding the _gasket-driver_ RPM whenever
there is a new _kernel_ published.

jenkins/updatecheck.toml

@@ -0,0 +1,13 @@
+[storage]
+dir = "/var/lib/updatecheck"
+
+[[watch]]
+packages = "kernel"
+
+[watch.on_update]
+url = "https://jenkins.pyrocufflink.blue/generic-webhook-trigger/invoke"
+coalesce = true
+
+[[watch.on_update.headers]]
+name = 'Token'
+value_file = '/run/secrets/updatecheck/token'