compare rolling ETF to session ETF, remove rolling ETF from workflow

[japhir]

currently the workflow calculates "session ETFs" for all runs that have the same etf_grp

• define good etf_grp for things that should be considered the same session in motu_metadata_parameters
• calculate ETFs
• compare ETF session correction to the rolling ETF (201 window size)
• remove calculations from _targets.R so that the whole workflow is faster