[Migration optimization] Add flag to state extraction program to output intermediate format instead of migrated checkpoint

[fxamacker]

Add flag to state extraction program (cmd/util/util) to output payloads instead of checkpoint file.

This can optimize migrations (Atree inlining and Cadence 1.0) if need to run 2 migration executables.

As one possible use case:

• 1st executable: run Atree Inlining migration with Cadence 0.42.x
• 2nd executable: run Cadence 1.0 migration with support for Atree Inlining

This is part of epic onflow/cadence#2983