The Estate Steward/Estate Chambermaids already sell drinks and food items so just use one of those if you're wanting to set up a bar in your personal house/FC house/apartment, as I do not see SE adding an actual bartender npc for housing, given this would potentially run afoul of restrictions on sales of alcohol depicted in media that exist in many countries that SE are required to abide by.

I don't agree with it, but it's just how it is and is something that cannot be changed (the /toast emote on the Mogstation could get around such restrictions by not necessarily stating it's alcohol in the mug, which of course it so clearly is, but that's another thing entirelly).

So really, just use the existing butler/maid npcs for your personal tavern staff, as SE will not implement actual bar staff as housing npcs, that's just being realistic.