They are different tenses. It's added is present tense. It was added is past tense, and it has been added is past perfect. The first would be a little unusual to use. You would probably only say that as soon as you had added something. 'It was added' would probably be used with a time phrase, e.g. last week, or 'after the meeting', or perhaps with a location 'it was added to the second branch'. The point of this sentence is to give the extra information. It has been added' would be used to describe the current state. It means that it is there - the addition has been done at some stage previously. It doesn't say when, or where, or why, possibly if that information is not know.