migrate app dataDir to volumes

migrations/schema.sql

@@ -93,7 +93,8 @@ CREATE TABLE IF NOT EXISTS apps(
     inboxDomain VARCHAR(128), // mailbox domain of this app
     label VARCHAR(128),     // display name
     tagsJson VARCHAR(2048), // array of tags
-    dataDir VARCHAR(256) UNIQUE,
+    storageVolumeId VARCHAR(128),
+    storageVolumePrefix VARCHAR(128),
     taskId INTEGER, // current task
     errorJson TEXT,
     servicesConfigJson TEXT, // app services configuration
@@ -104,6 +105,8 @@ CREATE TABLE IF NOT EXISTS apps(
 
     FOREIGN KEY(mailboxDomain) REFERENCES domains(domain),
     FOREIGN KEY(taskId) REFERENCES tasks(id),
+    FOREIGN KEY(storageVolumeId) REFERENCES volumes(id),
+    UNIQUE (storageVolumeId, storageVolumePrefix),
     PRIMARY KEY(id));
 
 CREATE TABLE IF NOT EXISTS appPortBindings(