My chicken breasts release a lot of fluid when cooked. How do I prevent this?

Most chicken breasts sold (at least the of the cheaper variety) that I have seen, say something about being infused with up to 15% chicken broth. My guess is that most of the water you are seeing is the added chicken broth.

So look at the packaging of the chicken breasts before you buy them. Most of the high quality chicken sold that I have seen do not say that they are infused with chicken broth.

I suggest massaging the meat with flour and letting it absorb it for some time, that is, until the flour absorbs moisture from the meat and changes color from white to yellow-ish, and becomes sticky. This should allow the meat to retain some of the water while cooking.

It sounds like you're buying a cheaper cut of meat - one that's likely been infused with water to plump and to rapidly chill the meat to a safe temperature after butchery. Look for packages that state 'air-chilled' instead.

Since every chicken farmer in America does it (plumping is the industry standard) you should look for a brand that says "no added water" or "no retained water". I have found only 2 brands that say this. One is at Harris Teeter super market.

The industry standard is 12%. That means you must assume all of the chicken is plumped unless it says otherwise. The problem with chicken that is pumped full of water is it never gets to the right temperature for a proper texture, instead it is rubbery and the real chicken flavor is washed away.
If you decide to brine your chicken it will have a hard time absorbing because it is already pumped full of flavorless salt water.

Desiccate the outside of the chicken with salt for about 20-60 mins to remove the excess water and then brush off the salt after to make sure it isn't too salty; this should help concentrate the flavour and remove some of the water.

Sear the outside of the chicken on HIGH heat with butter or oil to seal in the juices and flavour.

You can also try dredging the chicken in flour to give it a crust. Cook again in high heat with butter or oil to seal.

Personally I do BOTH the first two options to get a crisp crust and a juicy tender inside but you can very easily do all three.

The water infusion described above was news to me, but I have certainly observed this exact same problem when cooking chicken in a sauce (usually curries).

My solution (using cheap frozen chicken breasts that produce a ton of liquid) has been to cook the chicken separately – for example, grilling it on a BBQ or pan-frying it in a separate pan, or even boiling it in broth in a slow-cooker. You don't need to over-cook it, but this gets rid of the excess liquid and then you add it back into the sauce to simmer and you avoid watering the sauce down.