r/v-m-nginx: Proxy for other services too

The *metricspi* hosts several Victoria Metrics-adjacent applications.
These each expose their own HTTP interface that can be used for
debugging or introspecting state.  To make these accessible on the
network, the *victoria-metrics-nginx* role now configures `proxy_pass`
directives for them in its nginx configuration.

roles/victoria-metrics-nginx/defaults/main.yml

@@ -1 +1,10 @@
 victoria_metrics_server_name: '{{ ansible_fqdn }}'
+vm_nginx_proxy_paths:
+- path: /alertmanager/
+  url: http://[::1]:9093/
+- path: /vmagent/
+  url: http://[::1]:8429/
+- path: /vmalert
+  url: http://[::1]:8880
+- path: /blackbox_exporter/
+  url: http://[::1]:9115/