correlated_field.py: Implement offset in finalize

Allow for specifying either a Field/MultiField or a float as an offset
for the correlated field during `finalize`.
9 jobs for nifty6_cfm_offset in 9 minutes and 49 seconds (queued for 2 seconds)
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build_docker_from_cache

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  Test
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test_mpi

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test_serial

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run_bernoulli

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run_curve_fitting

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run_getting_started_1

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run_ipynb

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