Add support for hostAliases (#401)

### Description of the change

It is required to add custom mapping between hostnames and IP addresses for the gitea pods to be able to access external services like oauth providers or webhook servers.
It is common to take global variables for the entires and set them using hostAliases in the pod template.

### Benefits

Give us more flexibility when using gitea in various network environments.

### Applicable issues

- fixes #400

### Checklist

- [X] Parameters are documented in the `values.yaml` and added to the `README.md` using [readme-generator-for-helm](https://github.com/bitnami-labs/readme-generator-for-helm)

Co-authored-by: Taekyun Kim <tkq.kim@samsung.com>
Co-authored-by: pat-s <pat-s@noreply.gitea.io>
Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/401
Reviewed-by: pat-s <pat-s@noreply.gitea.io>
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.io>
Co-authored-by: podain77 <podain77@noreply.gitea.io>
Co-committed-by: podain77 <podain77@noreply.gitea.io>

README.md

@@ -591,6 +591,7 @@ gitea:
 | `global.imageRegistry`    | global image registry override                                            | `""`            |
 | `global.imagePullSecrets` | global image pull secrets override; can be extended by `imagePullSecrets` | `[]`            |
 | `global.storageClass`     | global storage class override                                             | `""`            |
+| `global.hostAliases`      | global hostAliases which will be added to the pod's hosts files           | `[]`            |
 | `replicaCount`            | number of replicas for the statefulset                                    | `1`             |
 | `clusterDomain`           | cluster domain                                                            | `cluster.local` |