DodoApp: Support volume requests

Users can define volumes section under app, and for each volume
corresponding env variable will be passed down to the application.

Change-Id: I8da9d5e1ca652cdb2f0196fcba1b6242064d057f
diff --git a/core/installer/app_configs/testapp.cue b/core/installer/app_configs/testapp.cue
index 2573c5c..8201ff6 100644
--- a/core/installer/app_configs/testapp.cue
+++ b/core/installer/app_configs/testapp.cue
@@ -6,6 +6,7 @@
 		subdomain: "testapp"
 		auth: enabled: false
 	}
+	volumes: data: size: "1Gi"
 }
 
 // do create app --type=go[1.22.0] [--run-cmd=(*default main.go)]