Accumulated Freezing Degree Day indicator should use offset_yearly time aggregation

[rmartz]

Because Accumulated Freezing Degree Day is affected by streaks of wintery weather, it is best suited to be evaluated across a contiguous winter (Similar to how Heat Wave Duration Index is best suited for a contiguous summer). Because it currently is the only indicator of its kind in that way, it should be specially configured to always use the offset_yearly time aggregation to provide the most accurate data to users.