Move domains field to managedCertificate block (#750)

**What this PR does / why we need it**:

**Which issue(s) this PR fixes**:

Fixes #

**Does this PR introduce a user-facing change?**:
<!--
If no, just write "NONE" in the release-note block below.
-->
```release-note
NONE
```

/cc @gkuga 
This PR was merged by Kapetanios.

manifests/pipecd/templates/managed-certificate.yaml

@@ -5,7 +5,7 @@ metadata:
   name: {{ include "pipecd.fullname" . }}
 spec:
   domains:
-  {{- range .Values.ingress.domains }}
+  {{- range .Values.managedCertificate.domains }}
   - {{ . }}
   {{- end }}
 {{- end }}

manifests/pipecd/values.yaml

@@ -10,15 +10,13 @@ backendConfig:
 
 managedCertificate:
   enabled: false
+  domains: []
 
 ingress:
   enabled: false
   annotations: {}
     # kubernetes.io/ingress.allow-http: "false"
     # kubernetes.io/ingress.global-static-ip-name: pipecd
-  domains: []
-    # - api.pipecd.dev
-    # - dev.pipecd.dev
 
 cors:
   enabled: true