Balancer runtime management capability improvement

[popduke]

1. allow inspection of the state of balancer instances via API
2. allow setting expected rules via API
3. reorganize traffic rules and landscape retrospection related APIs

[coveralls]

Pull Request Test Coverage Report for Build 16589427130

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 280 unchanged lines in 33 files lost coverage.
• Overall coverage decreased (-0.2%) to 63.048%

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Files with Coverage Reduction	New Missed Lines	%
org/apache/bifromq/apiserver/http/handler/AbstractTrafficRulesHandler.java	1	75.86%
org/apache/bifromq/apiserver/http/handler/GetServiceLandscapeHandler.java	1	93.33%
org/apache/bifromq/basecluster/memberlist/agent/Agent.java	1	95.16%
org/apache/bifromq/basecluster/util/RandomUtils.java	1	80.65%
org/apache/bifromq/basecrdt/core/internal/CausalCRDTInflater.java	1	92.21%
org/apache/bifromq/basekv/metaservice/IBaseKVMetaService.java	1	66.67%
org/apache/bifromq/basescheduler/Batcher.java	1	83.44%
org/apache/bifromq/mqtt/handler/MQTTPersistentSessionHandler.java	1	74.7%
org/apache/bifromq/apiserver/http/handler/GetSessionInfoHandler.java	2	86.96%
org/apache/bifromq/apiserver/http/HTTPRequestRouter.java	2	81.82%

Totals
Change from base Build 16462893977:	-0.2%
Covered Lines:	23544
Relevant Lines:	36056

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💛 - Coveralls