Update an existing ramp plan's configuration, including name, commitments, breakpoints, and non-export offsets.

Supplied billingAccountIDs, breakpoints, commitments, enumeratedValues, nonExportOffsetByMonth, and nonExportOffsetRecurring replace their complete collections/maps; entries are not merged. Omission retains existing values. Empty collections clear them where permitted, but billingAccountIDs must be nonempty. Breakpoints are normalized as part of the update.