Remove `stash`, `unstash` and `monitor` keys from the default inputs

[mbercx]

From #6826 (comment):

@khsrali one question: do we need to always have the stash and unstash keys in the metadata.options? Now for every CalcJob, even an empty builder will have these keys, e.g.:

from aiida.calculations.arithmetic.add import ArithmeticAddCalculation

ArithmeticAddCalculation.get_builder()

returns

Process class: ArithmeticAddCalculation
Inputs:
metadata:
  options:
    stash: {}
    unstash: {}
monitors: {}

(I have a similar question for the monitors, but I'll check that separately.)

My concern it that this makes the often already complicated inputs for processes even more complicated, harder to read, and also will make users wonder what these inputs are and why they are there.