Add placeholder function for converting from esa_step to esa_energy_step

[subagonsouth]

Change Summary

Overview

Added a placeholder function for where the algorithm for computing esa_energy_step. The function will eventually be updated to use the L1B housekeeping to correctly populate the data. See ticket #779

Updated Files

• imap_processing/hi/l1b/hi_l1b.py
  • Update the annotate direct events algorithm to call the new placeholder function
  • Add placeholder function for populating esa_energy_step. For now, copy the esa_step value.
• imap_processing/tests/hi/test_hi_l1b.py
  • Add test coverage for new placeholder function

closes: #1145