in consumer, support priority level

[wolfstudy]

Describe alternatives you've considered

Sets priority level for the shared subscription consumers to which broker gives more priority while dispatching messages. Here, broker follows descending priorities. (eg: 0=max-priority, 1, 2,..) In Shared subscription mode, broker will first dispatch messages to max priority-level consumers if they have permits, else broker will consider next priority level consumers. If subscription has consumer-A with priorityLevel 0 and Consumer-B with priorityLevel 1 then broker will dispatch messages to only consumer-A until it runs out permit and then broker starts dispatching messages to Consumer-B.

Consumer	PriorityLevel	Permits
C1	0	2
C2	0	1
C3	0	1
C4	1	2
C5	1	1

Order in which broker dispatches messages to consumers: C1, C2, C3, C1, C4, C5, C4

for specific functional descriptions, refer to: property level