Custom env vars for apps

Add a table and the install/configure routes. Initially, I thought
we can just keep the env vars in docker container but that doesn't
work since we create the container only later in apptask. And if the
container gets deleted we lose this information.

migrations/schema.sql

@@ -118,6 +118,12 @@ CREATE TABLE IF NOT EXISTS appAddonConfigs(
     value VARCHAR(512) NOT NULL,
     FOREIGN KEY(appId) REFERENCES apps(id));
 
+CREATE TABLE IF NOT EXISTS appEnvVars(
+    appId VARCHAR(128) NOT NULL,
+    name TEXT NOT NULL,
+    value TEXT NOT NULL,
+    FOREIGN KEY(appId) REFERENCES apps(id));
+
 CREATE TABLE IF NOT EXISTS backups(
     id VARCHAR(128) NOT NULL,
     creationTime TIMESTAMP,