fix: choose provider correctly (#7081)

fix no provider error in caption generate action

packages/backend/server/migrations/20240527095524_fix_prompt_schema/migration.sql

@@ -0,0 +1,8 @@
+/*
+  Warnings:
+
+  - Made the column `model` on table `ai_prompts_metadata` required. This step will fail if there are existing NULL values in that column.
+
+*/
+-- AlterTable
+ALTER TABLE "ai_prompts_metadata" ALTER COLUMN "model" SET NOT NULL;