Awesome.

Yes, you can definitely control your pond water level! If it is just black polypipe you can make a tee and connections using the barb fittings for that size of line. (You wouldn't think they would work if you are used to "normal" plumbing jobs, but they work just fine for unpressurized lines.)

Float valve installations are one option. Maybe search "float valve for cattle tank" for simple, inexpensive options.

If you don't like that option, then you might try a "timer" valve to introduce some water every day. (If the water level is getting too low, then just increase the run time for a few days.) I have that type of valve on some tanks that I have set up to control drip irrigation on some new tree plantings. The valves I have (discontinued) run for several months on a 9V battery. I just set them up to run X minutes every 24 hours.

If you choose that option, make sure you get the valve for low pressure applications. The ones that run off of your pressurized household lines do NOT work well with only a few feet of head like from a rain barrel.