Synchronous option for KeyValueStore

[rdev34]

Due to the asynchronous nature of KeyValueStore which uses callbacks, there are difficulties with organizing and structuring code that fetches multiple keys at once or certain keys in sequence. We can write simpler and more readable code with a synchronous option that would end up looking like this:

CreateThread(function()
    local value1 = KeyValueStore:Get({key = "Key1", synchronous = true})
    local value2 = KeyValueStore:Get({key = "Key2", synchronous = true})

    if value1 > value2 then
        print("my code looks so pretty!")
    end
end)

Note: This requires refactoring KVS:Get to use single arg table instead of positional args