feat(es_extended/server/functions): introduce does item and account exist

[Sloosi0502]

Description

Added feature to check if an item or an account does exist.

Motivation

Troubleshooting or error catching

Implementation Details

function

Usage Example

if ESX.DoesItemExist(item) then
    xPlayer.addInventoryItem(item, 1)
end

if ESX.DoesAccountExist(account) then
    xPlayer.addAccountMoney(account, 1)
end

[CLAassistant]

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