Add helper method for decoding deleted record

[byucesoy]

While working on DeletedRecord, we frequently need to find the record from its ubid. This commit adds a helper method for that.

[enescakir]

What do you think about adding it to the udec as a second option?
Probably we will run udec first and it will return nil, then we will run udec_deleted

Suggested change

	UBID.decode(*)
	end
	def udec_deleted(ubid)
	DeletedRecord.where(Sequel.pg_json(:model_values)["name"] => Sequel.pg_jsonb_wrap(UBID.parse(ubid).to_uuid)).first
	end
	UBID.decode(*) || DeletedRecord.where(Sequel.pg_json(:model_values)["name"] => Sequel.pg_jsonb_wrap(UBID.parse(ubid).to_uuid)).first
	end

[furkansahin]

I think we must add a gin index for this field. Simply querying deleted records in production is almost unbearable at this point.

[fdr]

it's also using almost all our space. Should we consider partitioning as well? How often are we digging in the ancient past? Not often, right?

GIN is perhaps the first thing to try, though the idea of a GIN over all (ever growing) history that has to get updated with every deletion makes me a little bit suspenseful. Just a bit.

[enescakir]

Shouldn't we filter by id instead of name?

Suggested change

	DeletedRecord.where(Sequel.pg_json(:model_values)["name"] => Sequel.pg_jsonb_wrap(UBID.parse(ubid).to_uuid)).first
	DeletedRecord.where(Sequel.pg_json(:model_values)["id"] => Sequel.pg_jsonb_wrap(UBID.parse(ubid).to_uuid)).first