Add support for metrics and pprof (#100)

Adds support for toggling support for `pprof` and metrics:

```yaml
gitea:
  pprofEnabled: true

  metrics:
    enabled: true
    serviceMonitor:
      enabled: true
```

Co-authored-by: josef <josef.nilsen@outlook.com>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/100
Reviewed-by: luhahn <luhahn@noreply.gitea.io>
Reviewed-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: JosefWN <josefwn@noreply.gitea.io>
Co-committed-by: JosefWN <josefwn@noreply.gitea.io>

templates/gitea/servicemonitor.yaml

@@ -0,0 +1,14 @@
+{{- if .Values.gitea.metrics.serviceMonitor.enabled -}}
+apiVersion: monitoring.coreos.com/v1
+kind: ServiceMonitor
+metadata:
+  name: {{ include "gitea.fullname" . }}
+  labels:
+    {{- include "gitea.labels" . | nindent 4 }}
+spec:
+  selector:
+    matchLabels:
+      {{- include "gitea.selectorLabels" . | nindent 6 }}
+  endpoints:
+  - port: http
+{{- end -}}