feat: export relation's query client

[adamcikado]

❓ Type of change

• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

Export relation's query client so it can be extended, e.g.:

import { HasManyQueryClient } from '@adonisjs/lucid/orm/relations'

HasManyQueryClient.prototype.sync = ... // custom sync logic