Undo mode for CumulusCI Insert

[prescod]

Please describe the nature of this feature request

• I'm interested in extensions to existing CumulusCI functionality (e.g., broader applicability of an existing Task or Flow).

Does your feature request solve a current problem? Please describe. As a contingency plan, a process should be available to safely delete all records created by CumulusCI without deleting the existing records already persisted in the target system

Describe the solution you'd like cci task run undo_insert

Additional context This was requested formally by an internal teams and informally many times.