feat(backend): Add database index for improved query performance (#10411)

This PR adds a database index to improve query performance based on
Supabase query performance insights and index recommendations. These
indexes target frequently queried columns and relationships to reduce
query execution time.

### Changes 🏗️
- Added index on `AgentNodeExecutionInputOutput.agentPresetId`

### Checklist 📋

#### For code changes:
- [x] I have clearly listed my changes in the PR description
- [x] I have made a test plan
- [x] I have tested my changes according to the test plan:
  - [x] Verified schema changes are valid Prisma syntax
- [x] Confirmed indexes target frequently queried columns based on
Supabase recommendations
  - [x] Ensured no duplicate indexes are created

#### For configuration changes:
- [x] `.env.example` is updated or already compatible with my changes
- [x] `docker-compose.yml` is updated or already compatible with my
changes
- [x] I have included a list of my configuration changes in the PR
description (under **Changes**)

autogpt_platform/backend/migrations/20250721073830_add_preset_index/migration.sql

@@ -0,0 +1,2 @@
+-- CreateIndex
+CREATE INDEX "AgentNodeExecutionInputOutput_agentPresetId_idx" ON "AgentNodeExecutionInputOutput"("agentPresetId");

autogpt_platform/backend/schema.prisma

@@ -411,6 +411,7 @@ model AgentNodeExecutionInputOutput {
   @@index([referencedByOutputExecId])
   // Composite index for `upsert_execution_input`.
   @@index([name, time])
+  @@index([agentPresetId])
 }
 
 model AgentNodeExecutionKeyValueData {