Plans for splitting up PROCESS_QUEUE table

[ibodrov]

We need to split the PROCESS_QUEUE table up.

In order to do that we need to plan some changes across several releases.

Here's the approximate plan:

• release 1.63.0:
  • create a new PROCESS_STATUS table:
    • INSTANCE_ID
    • CREATED_AT
    • CURRENT_STATUS
    • LAST_UPDATED_AT
  • create necessary indicies;
  • create a trigger to fill PROCESS_STATUS table in.
• release (+ 1 month from 1.63.0):
  • drop the trigger;
  • make PROCESS_QUEUE.CURRENT_STATUS and LAST_UPDATED_AT nullable, stop using those columns in the code;
  • (optionally) drop PROCESS_QUEUE.CURRENT_STATUS and LAST_UPDATED_AT columns.

[ibodrov]

cc @brig, @mtkunkel, @benbroadaway