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>

README.md

@@ -95,6 +95,16 @@ ROOT_URL = http://git.example.com
 SSH_DOMAIN = git.example.com
 SSH_LISTEN_PORT = 22
 SSH_PORT = 22
+ENABLE_PPROF = false
+```
+
+#### Metrics defaults
+
+The Prometheus `/metrics` endpoint is disabled by default.
+
+```ini
+[metrics]
+ENABLED = false
 ```
 
 ### External Database
@@ -278,6 +288,24 @@ kebab-case:
       username-attribute: CN
 ```
 
+### Metrics and profiling
+
+A Prometheus `/metrics` endpoint on the `HTTP_PORT` and `pprof` profiling endpoints on port 6060 can be enabled under `gitea`. Beware that the metrics endpoint is exposed via the ingress, manage access using ingress annotations for example.
+
+To deploy the `ServiceMonitor`, you first need to ensure that you have deployed `prometheus-operator` and its CRDs: https://github.com/prometheus-operator/prometheus-operator#customresourcedefinitions.
+
+```yaml
+gitea:
+  metrics:
+    enabled: true
+    serviceMonitor:
+      enabled: true
+
+  config:
+    server:
+      PPROF_ENABLED: true
+```
+
 ### Pod Annotations
 
 Annotations can be added to the Gitea pod.