Add moving average (by DataArray.rolling) to qlook commands

[ShinjiFujita]

Closes #186.

[astropenguin]

Thank you for the update! I would like to ask you to fix the following things:

• Order (position) of the option: rolling_time option is for analysis, so it should be placed under # options for analysis (above source_radius: str = "60 arcsec",). Could you move the line?
• Description of the option: Could you add a short description about the rolling_time option in the docstring?
• Which data to be rolled: It seems that da_sub is not suitable data to be rolled because its timestamps are no longer continuous. We discussed in a DESHIMA meeting that rolling should be applied just after loading a DEMS, i.e., applied to da = select.by(da, "state", exclude="GRAD").

[astropenguin]

Thank you for the fix! It looks good for me.