feat(preloader): add preloadOnce to preload a relationship only once

[zaosoula]

🔗 Linked issue

Similar to PR #1052 by @RomainLanz

❓ 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

Added a preloadOnce method to the query building using the same logic as the loadOnce

In our use case we allow the client to preload field using a query parameter $populate: string[]

this method is in a https://github.com/lookinlab/adonis-lucid-filter file

While doing so we sometimes also use preload in our services

If the client request find with the following payload

{
	"$populate": ["tenant.settings"],
	"id": 1
}

Without .preloadOnce

1. The filter will call query.preload("tenant", (subquery) => { subquery.preload('settings') })
2. The service will call query.preload("tenant") and override the callback
3. find will return the data with the tenant populated but without the tenant > settings

With .preloadOnce

1. The filter will call query.preload("tenant", (subquery) => { subquery.preload('settings') })
2. The service will call query.preloadOnce("tenant") and nothing will happen as tenant is already queued for preloading
3. find will return the data with the tenant populated and also tenant > settings populated

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[thetutlage]

Makes sense 👍