Use variable susbtitution in manifests

apps/prod/gitea/values.yaml

@@ -24,7 +24,7 @@ image:
 gitea:
   admin:
     existingSecret: gitea-admin-secret
-    email: "admin@example.com"
+    email: "${GITEA_ADMIN_EMAIL}"
   config:
     actions:
       ENABLED: true
@@ -40,8 +40,8 @@ gitea:
       TYPE: channel
     server:
       BUILTIN_SSH_SERVER_USER: git
-      ROOT_URL: https://git.example.com
-      DOMAIN: git.example.com
+      ROOT_URL: https://${GITEA_DOMAIN}
+      DOMAIN: ${GITEA_DOMAIN}
       SSH_CREATE_AUTHORIZED_KEYS_FILE: false
       LANDING_PAGE: explore
     service: