Remove vertx from KafkaAutoRebalanceReconciler

[ShubhamRwt]

Type of change

• Refactoring

Description

This PR remove the use of vertx completely from the KafkaAutoRebalanceReconciler and make use of the of the Java classes(CompletionStage and CompletableFuture).

Checklist

Please go through this checklist and make sure all applicable tasks have been done

• Update documentation
• Update CHANGELOG.md (if present)
• Reference relevant issue(s) and close them after merging
• Write tests
• Make sure all tests pass
• Try your changes inside a Kubernetes cluster, not just from unit tests
• AI assistance was used to create this PR (see the Strimzi AI policy)

[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues
✅	Code Security	0	0	0	0	0 issues

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[codecov]

Codecov Report

❌ Patch coverage is 79.10448% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.34%. Comparing base (24f9fcc) to head (6e39304).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...rator/assembly/KafkaAutoRebalancingReconciler.java	78.46%	13 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main   #13064      +/-   ##
============================================
+ Coverage     80.33%   80.34%   +0.01%     
- Complexity     6522     6529       +7     
============================================
  Files           343      343              
  Lines         22695    22703       +8     
  Branches       3079     3081       +2     
============================================
+ Hits          18231    18240       +9     
+ Misses         3250     3249       -1     
  Partials       1214     1214              

Files with missing lines	Coverage Δ
...uster/operator/assembly/KafkaAssemblyOperator.java	84.47% <100.00%> (ø)
...rator/assembly/KafkaAutoRebalancingReconciler.java	81.70% <78.46%> (+0.20%)	⬆️

... and 1 file with indirect coverage changes

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[tinaselenge]

This seems to be an additional logic. Doesn't whenComplete already propagates the original result? so if maybeRebalance fails, the returned future fails with the same error and If it succeeds, the returned future succeeds? Do we need to manually check it again?