feat: make feature flag image optional (#17679)

Prevent layout shift when no image is provided for a feature flag

## Before


https://github.com/user-attachments/assets/b1a98da9-1208-46f7-9fc6-9c34a9012c02

## After 


https://github.com/user-attachments/assets/ed12df0c-1651-4fc9-a0e7-60f5fb1533a4

packages/twenty-server/src/engine/core-modules/client-config/client-config.entity.ts

@@ -108,8 +108,8 @@ export class PublicFeatureFlagMetadata {
   @Field(() => String)
   description: string;
 
-  @Field(() => String, { nullable: false, defaultValue: '' })
-  imagePath: string;
+  @Field(() => String, { nullable: true })
+  imagePath?: string;
 }
 
 @ObjectType()