Improving DRY principle support on gitea Ingress host name (#498)

### Description of the change

Introducing `tpl` function on variables related to hostname in `./templates/gitea/ingress.yaml`

### Benefits

The change is intending to support the following syntax in a values.yaml such as:
```
global:
  giteaHostName: "gitea.my-org.com"

ingress:
  enabled: true
  hosts:
    - host: "{{ .Values.global.giteaHostName }}"
      paths:
        - path: /
          pathType: Prefix
  tls:
      - secretName: gitea-tls
        hosts:
          - "{{ .Values.global.giteaHostName }}"
```

### Possible drawbacks

N/A

### Applicable issues

N/A

### Additional information

N/A

Reviewed-on: https://gitea.com/gitea/helm-chart/pulls/498
Reviewed-by: justusbunsi <justusbunsi@noreply.gitea.com>
Co-authored-by: Ceddaerrix <ceddaerrix@noreply.gitea.com>
Co-committed-by: Ceddaerrix <ceddaerrix@noreply.gitea.com>

unittests/deployment/ingress-configuration.yaml

@@ -0,0 +1,23 @@
+suite: ingress template
+release:
+  name: gitea-unittests
+  namespace: testing
+templates:
+  - templates/gitea/ingress.yaml
+tests:
+  - it: hostname using TPL
+    set:
+      global.giteaHostName: "gitea.example.com"
+      ingress.enabled: true
+      ingress.hosts[0].host: "{{ .Values.global.giteaHostName }}"
+      ingress.tls:
+        - secretName: gitea-tls
+          hosts:
+            - "{{ .Values.global.giteaHostName }}"
+    asserts:
+      - equal:
+          path: spec.tls[0].hosts[0]
+          value: "gitea.example.com"
+      - equal:
+          path: spec.rules[0].host
+          value: "gitea.example.com"