Steamed chicken soup
Actual chicken soup is based on chicken stock which is made by simmering a chicken carcass for several hours, usually with stick veg and a few herbs. 

This long cooking breaks down the collagen in the bones, skin and cartilage, turning it into gelatin and extracting a lot of flavour. 

The steaming water should be perfectly safe to eat but definitely isn't the same thing as chicken stock. 

Maybe use it to cook rice or noodles to go with the chicken or if the breasts cam e off whole chicken then add it to the carcass to make stock if you want. But in reality it probably doesn't have that much flavour and probably isn't worth keeping unless you have an immediate use for it. 

A an aside one of the great thing about poultry in general is that you can use the whole of the bird to make several dishes. 

The breast meat provides good texture, the legs and thigh meat is moist and flavoursome and good for pies and stews, the carcass can be used for soup and the wings and timings can be turned into a tasty sauce or gravy.