Use javascript functions for prompt completions instead of templated json

prisma/migrations/20230714004556_add_construct_fn_to_prompt_variant/migration.sql

@@ -0,0 +1,15 @@
+-- 1. Add a nullable constructFn column
+ALTER TABLE "PromptVariant"
+ADD COLUMN "constructFn" TEXT;
+
+-- 2. Populate constructFn based on the config column
+UPDATE "PromptVariant"
+SET "constructFn" = 'prompt = ' || "config"::text;
+
+-- 3. Remove the config column
+ALTER TABLE "PromptVariant"
+DROP COLUMN "config";
+
+-- 4. Make constructFn not null
+ALTER TABLE "PromptVariant"
+ALTER COLUMN "constructFn" SET NOT NULL;