I can’t imagine how it wouldn’t have been. I’m pretty sure the rules around what is kosher and not were set a few thousand years before infant formula was invented, and so if it wasn’t kosher then literally every Jewish person would have been breaking Jewish law until they could move onto solid foods.
Small children (under 6-7) are exempt from Jewish law. Making breast milk kosher isn’t exactly neccsery, but it makes things much easier (how to keep it, making sure it won’t get mixed with other foods by mistake, what happened if it does etc.) The neat part is that breast milk isn’t considered milk accordingly to Jewish law, so it can be drunk with/right after/before eating meat (otherwise forbidden). This means a person can, and I know at least one who actually did, add breast milk to their coffee after eating meat.
PSA: it stops being kosher if you cook the baby in it, so… don’t do that?
[Sorry for the silly joke, I couldn’t resist.]
