Remove thanosSelector and expose mixin._config.thanos config variable for thanos sidecar

This commit removes existing `thanosSelector` and exposes a single config variable `mixin._config.thanos` to customize thanos sidecar mixins. It follows same structure as d2d74dac98/mixin/config.libsonnet

Signed-off-by: Arunprasad Rajkumar <arajkuma@redhat.com>

jsonnet/kube-prometheus/components/prometheus.libsonnet

@@ -34,7 +34,15 @@ local defaults = {
     _config: {
       prometheusSelector: 'job="prometheus-' + defaults.name + '",namespace="' + defaults.namespace + '"',
       prometheusName: '{{$labels.namespace}}/{{$labels.pod}}',
-      thanosSelector: 'job="thanos-sidecar"',
+      thanos: {
+        targetGroups: {
+          namespace: defaults.namespace,
+        },
+        sidecar: {
+          selector: 'job="thanos-sidecar"',
+          thanosPrometheusCommonDimensions: 'namespace, pod',
+        },
+      },
       runbookURLPattern: 'https://runbooks.prometheus-operator.dev/runbooks/prometheus/%s',
     },
   },
@@ -65,12 +73,8 @@ function(params) {
     (import 'github.com/thanos-io/thanos/mixin/alerts/sidecar.libsonnet') +
     (import 'github.com/kubernetes-monitoring/kubernetes-mixin/lib/add-runbook-links.libsonnet') + {
       _config+:: p._config.mixin._config,
-      targetGroups: {},
-      sidecar: {
-        selector: p._config.mixin._config.thanosSelector,
-        thanosPrometheusCommonDimensions: 'namespace, pod',
-        dimensions: std.join(', ', ['job', 'instance']),
-      },
+      targetGroups+: p._config.mixin._config.thanos.targetGroups,
+      sidecar+: p._config.mixin._config.thanos.sidecar,
     },
 
   prometheusRule: {