[RIP-19] Pop Consuming (submodule "broker")

[ayanamist]

Make sure set the target branch to develop

What is the purpose of the change

This is "broker" submodule of contribution for RIP-19

Brief changelog

• Add QueryAssignment processor to control whether using pop mode or not.
• Add core Pop/Ack/ChangeInvisible interface
• Add pop consuming implementation using ScheduleService of store

Verifying this change

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[coveralls]

Coverage decreased (-0.3%) to 51.086% when pulling d54629c on ayanamist:dev_pop_consume into ea36854 on apache:pop_consumer.

[vongosling]

Do not introduce this older(2015) dependency, you could check guava's MapMaker or CacheBuilder. Or, use Caffeine.

[vongosling]

what is pop semantic? Common Queue Operations do not include pop except the special dequeue. Such a name can be confusing. IMO, We should use some common names in the industry. such as poll/pull, peek, push, and so on.