Create independent code for generating restarts from existing runs

[aidanheerdegen]

The COECMS access-esm historical configuration has some included scripts for creating payu compatible inputs from previous experiments

https://github.com/coecms/access-esm/blob/historical/warm-start.sh

The intention is that this code be extracted from within the payu configuration and made available separately. Probably in it's own repository with testing and documentation.