Add macro for scheduler directive for use in custom schedulers

[deardooley]

Issue summary

When creating custom directives in queue definitions of systems with CUSTOM_* scheduler types, there is no macro for the appropriate directive for the given scheduler. It would make things easier on novice users to have a token they can use in leu of remembering the value.

What platform services are impacted?

• [X ] Systems

To which tenant does this issue apply?

Community - https://api.agaveplatform.org

What version of the platform are you using?

2.2.14

Steps to recreate the issue

Expected behavior

A token such as, SYSTEM_SCHEDULER_DIRECTIVE could be used in the queue.customDirectives field.

Actual behavior

not currently supported