Allow minutes_per_sim to be less than a minute.

Is your feature request related to a problem? Please describe.
ResStock simulation time has improved a lot over time and based on some empirical data in Eagle test runs, it is now about 1/3 mintues. However, minutes_per_sim only takes integer value.

buildstockbatch/buildstockbatch/schemas/v0.3.yaml

Line 42 in f37754c

minutes_per_sim: int(max=480, required=False)

Describe the solution you'd like
Change the argument from minutes_per_sim to seconds_per_sim to go below minute level.

Describe alternatives you've considered
We can just use 1 minute and just deal with getting larger walltime than necessary. However, this will cause unnecessary scheduling wait.

Additional context
Add any other context or screenshots about the feature request here.

from @nmerket: Keep it minutes_per_sim but make it float to maintain backward compatibility.