Fix testHAProxyModeConnectionWorks is flaky

[gaobinlong]

Description

This PR fixes the flaky test testHAProxyModeConnectionWorks in RemoteClustersIT, from the gradle check log, we can see that the test case testProxyModeConnectionWorks always succeeds but the case testHAProxyModeConnectionWorks fails, the haproxy service haproxy:9600 provides a reversed proxy for opensearch-2:9300, opensearch-2:9300 is OK but haproxy:9600 cannot be accessed, so the only reason is that the haproxy service is not available at that time, maybe caused by that haproxy starts before opensearch-2, and the domain opensearch-2 is not ready, so haproxy exits with error:

2024-09-26 14:03:42 [ALERT] 269/060342 (1) : parsing [/usr/local/etc/haproxy/haproxy.cfg:22] : 'server default' : could not resolve address 'opensearch-2'.
2024-09-26 14:03:42 [ALERT] 269/060342 (1) : Failed to initialize server(s) addr.

Since haproxy depends on opensearch-2, so we should add a depends_on attribute for the haproxy service in the docker-compose.yml, and also add healthcheck for it to make sure the haproxy service is ready before the tests execute.

Related Issues

#14599

Check List

- [ ] Functionality includes testing.
- [ ] API changes companion pull request created, if applicable.
- [ ] Public documentation issue/PR created, if applicable.

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[github-actions]

✅ Gradle check result for def25bd: SUCCESS

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.96%. Comparing base (d510b12) to head (df2e1fe).
Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #16087      +/-   ##
============================================
+ Coverage     71.91%   71.96%   +0.04%     
- Complexity    64420    64424       +4     
============================================
  Files          5281     5281              
  Lines        301228   301228              
  Branches      43519    43519              
============================================
+ Hits         216643   216788     +145     
+ Misses        66835    66602     -233     
- Partials      17750    17838      +88     

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[github-actions]

❌ Gradle check result for ea53d79: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for ea53d79: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions]

❌ Gradle check result for ea53d79: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[reta]

Thanks @gaobinlong , I think you may need to rebase against main

[github-actions]

✅ Gradle check result for df2e1fe: SUCCESS