[improve][broker] Avoid logging errors when there is a connection issue during subscription.

[RobertIndie]

Motivation

The broker currently logs an error if there's a temporary connection issue:

[configuration-metadata-store-14-1] ERROR org.apache.pulsar.broker.service.persistent.PersistentTopic - [xxx] Failed to create subscription: xxxx
java.util.concurrent.CompletionException: org.apache.pulsar.broker.service.BrokerServiceException: Connection was closed while the opening the cursor 

We can change this to a warning log level. This way, it won't clutter the broker log, and we can still track connection issues.

Modifications

• Introduce a new Expcetion BrokerServiceException.ConnectionClosedException to track the connection closed error
• Avoid logging errors when there is a connection issue during subscription.

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Does this pull request potentially affect one of the following parts:

If the box was checked, please highlight the changes

• Dependencies (add or upgrade a dependency)
• The public API
• The schema
• The default values of configurations
• The threading model
• The binary protocol
• The REST endpoints
• The admin CLI options
• The metrics
• Anything that affects deployment

Documentation

• doc
• doc-required
• doc-not-needed
• doc-complete

Matching PR in forked repository

PR in forked repository:

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 74.21%. Comparing base (bbc6224) to head (f544b90).
Report is 884 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #23939      +/-   ##
============================================
+ Coverage     73.57%   74.21%   +0.63%     
+ Complexity    32624    31802     -822     
============================================
  Files          1877     1853      -24     
  Lines        139502   143740    +4238     
  Branches      15299    16336    +1037     
============================================
+ Hits         102638   106675    +4037     
+ Misses        28908    28656     -252     
- Partials       7956     8409     +453     

Flag	Coverage Δ
inttests	27.02% <0.00%> (+2.44%)	⬆️
systests	23.20% <0.00%> (-1.13%)	⬇️
unittests	73.73% <100.00%> (+0.88%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
.../pulsar/broker/service/BrokerServiceException.java	87.17% <100.00%> (+1.21%)	⬆️
...oker/service/nonpersistent/NonPersistentTopic.java	70.44% <ø> (+0.98%)	⬆️
...sar/broker/service/persistent/PersistentTopic.java	79.80% <100.00%> (+1.34%)	⬆️

... and 1031 files with indirect coverage changes