[GEN-1240] Add grs toggle

[rxu17]

Purpose: This PR is a draft PR. Majority of the code design is present. At times we would like to use the data dictionary (dd) as the primary mapping for a dataset over the combined mapping of dd and global response set (grs) for particular cohorts. This PR adds the ability to specify a use_grs parameter for whether we should use grs or not for the cohort.

This is specific only to the merge_and_decode step. This is the 1st PR in a series. See 2nd PR in series

Changes:

• Added production and use_grs parameters and logic to support that
• Added helper functions get_global_response_set and get_prov_used for easier testability and incorporation of the use_grs param

Testing:

• Unit tests (still in progress)
• Run merge_and_decode step with use_grs on staging and compare to production run in develop (should be the same result)
• Run merge_and_decodestep **without**use_grs` and compare to production run in develop (should have mapping differences)