Make BrokerSetAwareGoal configurable to accept partition coloring

[CCisGG]

This PR resolves #1862 .

As in the issue described, there are 2 solutions:

1. Make this goal easily extendable, and users can create a new goal reusing the code of this goal
2. Make this goal configurable.

@efeg originally suggests that we'd better have a new goal, but after consideration, I think make it configurable is a cleaner solution. With this new configuration "allow.partition.level.broker.set.aware", only minimal code changes are needed.

@efeg Please feel free to comment on any benefits of creating a new goal if you think that's better.

[mohitpali]

Did an initial quick pass. I will give it another go again.

[mohitpali]

Instead of doing this i would recommend introducing inheritance.

1. Introduce a configuration - broker.set.awareness.level=partition
   We can have only two choices - partition and topic
2. The Level can be picked from an ENUM so that no other level is allowed.
3. The default value of this configuration can be set to level topic.
4. Introduce an interface called BrokerSetAwarenessValidator
5. Implement two implementations TopicLevelBrokerSetAwarenessValidator and PartitionLevelBrokerSetAwarenessValidator
6. Based on configuration set, the instance of the BrokerSetAwarenessValidator will be chosen.
7. From here just call brokerSetAwarenessValidator.validate(partitions)

[mohitpali]

You could also just introduce the validate() method in th ENUMs (with values PARTITION and TOPIC )

    private enum BrokerSetAwarenessLevel {
        TOPIC {
            public void validate(Partitions p) {
                // do something
            }
        },
        PARTITION {
            public void validate(Partitions p) {
                // do something different
            }
        }

[mohitpali]

I would not use word coloring since it may be confusing. We have been referring to it as brokerserAwareness