Currently, backend options are parsed in the yaml parser.
This has some issues:
- backend specific code should be in the backend folders
- it is not possible to add backend options for backends added via
addons
This add a simple implementation of requests/limits for individual
steps. There is no validation of what the resource actually is beyond
checking that it can successfully be converted to a Quantity, so it can
be used for things other than just memory/CPU.
close#1809
