That is almost certainly a 6 to 8 week old Cornish Cross meat bird that was in its way to slaughter. I don't know what vaccinations it has had. It has come from a very tight biosecurity place so it is unlikely to be carrying many diseases though you can't rule out Coccidiosis. There is a better chance that your existing flock will give it something than that it will give them anything, but you never know.
As a CC it has been bred to grow quickly and be slaughtered about now. Some people have been able to keep CC alive for a couple of years but that is pretty rare. Usually they eat themselves to death fairly soon. They grow so big so fast that their bodies cannot handle it. Often you need to restrict feed to keep it form growing so big and so fast. That can be hard to do when it is with other chickens.
Then you have the problem that it is still a chick. It can be very hard to integrate a chick, especially a singe chick, with adults. You can read up on the various techniques people use to try to integrate them but it is not always easy.
In my opinion, it is better to eat it now or to give it to someone that will eat it than to try to keep it alive. It is highly likely its quality of life will soon go downhill. You can always try but I would not expect a good outcome.
