- update Job interface to introdcue MaxCurrency method for declaring the max currency of the specified job
- change the downstream jobs to implement the new interface method
  - GC and sample jobs are set to 1
  - other jobs are set to 0 that means unlimited
- add max currency optiot when doing job registration
- resolve issue #11586
  - probably resolve issue #11281
  - resolve issue #11570

Signed-off-by: Steven Zou <szou@vmware.com>