Support deleted object in ledger_entry

[shawnxie999]

Summary

Modifying the ledger_entry API as follows:

New Request Parameter

Field Name	Type	Description
include_deleted	️boolean	(Optional) If set to true and the queried object has been deleted, return its complete data prior to its deletion. If set to false or not provided and the queried object has been deleted, return objectNotFound (current behavior) .

New Response Parameter

Field Name	Type	Description
deleted_ledger_index	number	(Optional) Indicates the ledger index at which the object was deleted.

Motivation

Currently, ledger_entry API returns objectNotFound if the object has been deleted. But perhaps someone may want to find the object data before its deletion, without the need to dig through transaction history to find the index at which this particular object was deleted.

I think clio can introduce an improved ledger_entry API with the a change - rather than returning objectNotFound for a deleted object, it would return the complete object data prior to its deletion, as well as an additional field to indicated the ledger index at which the object wad deleted.

This is useful it for something like XRPL explorer. For example, if I create a MPT page that queries ledger_entry, it would work fine as long as the MPT is not destroyed. However, after the MPT is destroyed, the MPT page will no longer be available because ledger_entry will now return objectNotFound. This would result in suboptimal experience in the explorer. This would improve the user experience on explorers in the long term, as explorer adds new page for each object type.