[improve][broker] PIP-307: Add proxy support for Java client

[dragosvictor]

PIP-307

Motivation

PRs #21408 and #21682 implemented producer/consumer support as per the new load balancer transfer mechanism, described by PIP-307, but both assumed that the clients were directly connected to the brokers. This PR implements the respective functionality when connections are made via the Pulsar proxy.

Modifications

• Proxying information is determined by the LookupService.getBroker implementations but is not forwarded to the outside callers. The PR changes this method's signature to return a new LookupTopicResult object, that contains all the pertinent information and allows for ease of extension in the future.
• Cache the proxying information (a boolean flag only) in ConnectionHandler and use it when the connection is closed with a broker URL redirection.

Verifying this change

• Make sure that the change passes the CI checks.

This change added tests and can be verified as follows:

• Added proxy producer/consumer test, verifying that disconnecting the clients respects the assigned URL logical address as well as the proxy physical address. Verified test stability by running it 100 times in the CI runner.
• Added a test to verify the clients fall back to direct broker connections when the proxy service drops. Note that the test does not mandate a service URL change in the client. Instead, it resolves the URL to the proxy the first time and to the broker the second time. Verified for stability by running it 100 times.

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: (dragosvictor#3)

[github-actions]

@dragosvictor Please add the following content to your PR description and select a checkbox:

- [ ] `doc` <!-- Your PR contains doc changes -->
- [ ] `doc-required` <!-- Your PR changes impact docs and you will update later -->
- [ ] `doc-not-needed` <!-- Your PR changes do not impact docs -->
- [ ] `doc-complete` <!-- Docs have been already added -->

[codecov-commenter]

Codecov Report

Attention: 5 lines in your changes are missing coverage. Please review.

Comparison is base (8beac8b) 73.42% compared to head (a1e4810) 73.39%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master   #21789      +/-   ##
============================================
- Coverage     73.42%   73.39%   -0.04%     
- Complexity    32795    32797       +2     
============================================
  Files          1897     1898       +1     
  Lines        140656   140668      +12     
  Branches      15491    15492       +1     
============================================
- Hits         103282   103239      -43     
- Misses        29297    29353      +56     
+ Partials       8077     8076       -1     

Flag	Coverage Δ
inttests	24.18% <53.12%> (-0.07%)	⬇️
systests	24.72% <53.12%> (-0.13%)	⬇️
unittests	72.69% <84.37%> (-0.01%)	⬇️

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

Files	Coverage Δ
...tion/buffer/impl/TransactionBufferHandlerImpl.java	67.08% <100.00%> (ø)
...e/pulsar/client/impl/BinaryProtoLookupService.java	82.53% <100.00%> (ø)
...g/apache/pulsar/client/impl/HttpLookupService.java	81.25% <100.00%> (ø)
...g/apache/pulsar/client/impl/ConnectionHandler.java	86.77% <88.88%> (-0.52%)	⬇️
...g/apache/pulsar/client/impl/LookupTopicResult.java	80.00% <80.00%> (ø)
...rg/apache/pulsar/client/impl/PulsarClientImpl.java	74.30% <72.72%> (+0.19%)	⬆️

... and 61 files with indirect coverage changes