It's such a grey area to define "stealing" your electricity when it's included in an agreement.
In any rental you really can't modify any wiring and certainly can't increase your supply legally, meaning the miners you could run *safely* would be relatively paltry and the consumption pretty low, not to mention the fact you are averaging your consumption with a whole building and I have a hard time really calling it theft.
All that said, doing anything of the sort without consulting the landlord is a risky venture as I'm sure some would see it as grounds for eviction (operating a business in the unit, wiring/fire concerns, etc.)