Return template parameters in consistent order (#2975)

* return parameters from Terraform provisioner in sorted order

* persist parameter indices in database and return them in correct order from API

* don't re-sort parameters by name when creating templates

coderd/database/migrations/000029_variable_order.down.sql

@@ -0,0 +1 @@
+ALTER TABLE parameter_schemas DROP COLUMN index;

coderd/database/migrations/000029_variable_order.up.sql

@@ -0,0 +1,15 @@
+-- temporarily create index column as nullable
+ALTER TABLE parameter_schemas ADD COLUMN index integer;
+
+-- initialize ordering for existing parameters
+WITH tmp AS (
+	SELECT id, row_number() OVER (PARTITION BY job_id ORDER BY name) AS index
+	FROM parameter_schemas
+)
+UPDATE parameter_schemas
+SET index = tmp.index
+FROM tmp
+WHERE parameter_schemas.id = tmp.id;
+
+-- all rows should now be initialized
+ALTER TABLE parameter_schemas ALTER COLUMN index SET NOT NULL;