A config option to change whether or not Sea Serpents can despawn on Peaceful mode

[SarthDidious]

A small change that I think could be nice for some people. I sometimes like to capture Sea Serpents and stick them in tanks (depending on the size) for a highly aggressive "pet". I recently found out that they despawn on Peaceful because I had to switch it on to despawn a ton of mobs around my base that were causing a ton of lag and my poor serpent got caught in the crossfire and was despawned. It would be nice to add a config option for this, as I can see other people possibly doing something similar and hopefully help people avoid a similar issue that I had.