Allows to skip Ensemble Tracker for ZookeeperConfiguration to allow connecting to HA enabled Zookeeper clusters in Kubernetes

[linghengqian]

Fixes #2072.

Changes proposed in this pull request:

• Allows to skip Ensemble Tracker for ZookeeperConfiguration to allow connecting to HA enabled Zookeeper clusters in Kubernetes. See https://issues.apache.org/jira/browse/FLINK-31780 and https://issues.apache.org/jira/browse/CURATOR-568 .
• If the HA enabled Zookeeper clusters are hidden under a virtual IP of Kubernetes, the Zookeeper Client can return a URL during Ensemble Tracking, which will cause an unresolved host exception within the Curator Framework. At the ElasticJob level, this will cause a cluster restart.
• Updates documentation to match variable naming conventions in https://github.com/apache/zookeeper/blob/release-3.9.2/zookeeper-server/src/test/java/org/apache/zookeeper/JaasConfiguration.java .
• Also fixes error: Invalid config event received #1812 .

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 79.58%. Comparing base (a8ba448) to head (af11823).
Report is 53 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #2458      +/-   ##
============================================
- Coverage     80.10%   79.58%   -0.53%     
+ Complexity     1113     1106       -7     
============================================
  Files           204      204              
  Lines          3821     3810      -11     
  Branches        445      444       -1     
============================================
- Hits           3061     3032      -29     
- Misses          570      586      +16     
- Partials        190      192       +2     

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