[YUNIKORN-864] update design documentation with new interface

[manirajv06]

update scheduler core design documentation with new interface

[wilfred-s]

Based on the comment in the top of the document I think we should not update the scheduler_core_design.md at all: caution message in the doc
The messages processing has been simplified with the removal of the scheduler cache and most, if not all, of the document is obsolete. We should really start work on YUNIKORN-495 to get this fixed.

[manirajv06]

Ok. Let me give a try on YUNIKORN-495

[manirajv06]

@wilfred-s as discussed offline, created a new doc to describe interface message simplification, code flow analysis based on message changes, breaking shim dependency etc. Please take a look. Yes, we will need to revert previous commit done on Scheduler Cache design doc and we may need to add a caution header to Scheduler cache removal design doc to refer to this new doc.

[wilfred-s]

I have reverted the file that we do not maintain anymore.

[wilfred-s]

LGTM