[FEATURE] Add flag support to destroy seedkit

[dgraeber]

Currently, on any destroy call (seedfarmer destroy or seedfarmer apply with modules removed) SF does NOT destroy the seedkit - it is hard-coded to always retain the seedkit. This was implemented in this manner to prevent user errors and to gather more info about this use case.

We have introduced the --update_seedkit flag to the apply command. We should add a --destroy-seedkit flag to force the end user to consciously destroy the seedkit, and wind that thru the destroy method calls. Leave this as set to TRUE (leaving the seedkit intact) unless otherwise specified.

[dgraeber]

References in deployment_commands.py

• add the flag to the cli on destroy
• leverage the parameter to the destroy command method (currently called retain_seedkit)
• add the parameter to the destroy_deployment method
• remove the hardcoded value at line 546 - retain_seedkit=True
• hard-code the value to retain_seedkit=True on the apply command (ALWAYS!!!)