Is it better to grind off the whole blade or should I find someone to add metal and then sharpen it again?
Grinding the blade down that much would potentially change the shape of the blade. Due to the full depth bolster you would have to either try to reshape the bolster as well or create a blade that tapered very differently. The knife is an Oxo Good Grips 8” chefs knife which sells for around £20. It’s difficult to see that either of your options would be as effective as replacing the knife, unless it has sentimental value.
I had the same happen to me because I was in a hurry and cut frozen cheese thus being in the same situation as you.
I brought the knife to a professional to have it sharpened and he did a great job of grinding the blade evenly. That was 5 years ago and the knife is still serving me well.
He asked 15€ to do the job, but that was a fraction of what a new knife would have cost me. So if you have the tools and knowledge of doing it yourself: Grind the blade! Otherwise, bring it to a professional; it's not an easy job!