Update CERF output to include retired power plants and all operational power plants

[kmongird]

Current CERF configuration: Output DataFrame only includes the retirement date of newly sited power plants based on plant lifetime.

Desired updates:

1. Change CERF output to include all operational power plants as an optional parameter. This would include historical (non CERF-sited, non-retired) power plants, historical (non-retired) CERF-sited power plants, and newly sited power plants. This will require initializing CERF with an input file of operational power plants that are on the ground prior to any new capacity expansion plans, tracking their expected retirement, and tracking previous CERF sitings.

2. Produce a second output DataFrame of power plants that have been retired in the last timestep.