swh: only make ServiceMonitors match services in the current namespace

Generating ServiceMonitors in each namespace for services in all namespaces creates n**2 targets in prometheus. Each of these targets ends up being a duplicate of n-1 others, which generates prometheus warnings about out of order samples.

helm diff output:

------------- diff for swh/values/default.yaml -------------

--- /tmp/swh-chart.swh.q3avXeRk/default.yaml.before	2023-11-14 18:11:04.528019839 +0100
+++ /tmp/swh-chart.swh.q3avXeRk/default.yaml.after	2023-11-14 18:11:04.624021242 +0100
@@ -275,11 +275,12 @@
   namespace: swh
 spec:
   endpoints:
   - path: /metrics
     port: http
     interval: 10s
   selector:
     matchLabels:
       app: prometheus-statsd-exporter
   namespaceSelector:
-    any: true
+    matchNames:
+      - swh