control-plane: avoid duplicate CreateTopics requests for existing topics

[jijo-OO7]

Fixes #4406

Proposed Changes

• Make CreateTopicIfDoesntExist idempotent by checking Kafka metadata before creating topics.
• Avoid repeated CreateTopics requests and error responses during steady-state reconciliation.
• Update unit tests and mocks to reflect the new DescribeTopics first behavior.
• This change avoids repeated mutating CreateTopics requests by checking topic existence via Kafka metadata before creating.
• While this still involves a read call to Kafka, it removes unnecessary write requests and error responses in steady state reconciliation.

[knative-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: jijo-OO7
Once this PR has been reviewed and has the lgtm label, please assign leo6leo for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[codecov]

Codecov Report

❌ Patch coverage is 84.61538% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 36.19%. Comparing base (38083e7) to head (e5a1756).
⚠️ Report is 64 commits behind head on main.

Files with missing lines	Patch %	Lines
control-plane/pkg/kafka/topic.go	84.61%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #4654      +/-   ##
============================================
+ Coverage     28.83%   36.19%   +7.35%     
- Complexity        0      901     +901     
============================================
  Files           294      403     +109     
  Lines         16172    20011    +3839     
  Branches          0      342     +342     
============================================
+ Hits           4664     7243    +2579     
- Misses        11053    12128    +1075     
- Partials        455      640     +185     

Flag	Coverage Δ
java-unittests	67.15% <ø> (?)

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

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[jijo-OO7]

This change makes topic creation idempotent by checking topic metadata before issuing CreateTopic.
As a result, some existing unit/integration tests that assume CreateTopic is always called are currently failing and need their mocks updated to expect DescribeTopics.
I’m working through updating those test fixtures so they reflect the new behavior. Feedback on the approach is welcome.

[jijo-OO7]

/retest-required

[jijo-OO7]

@Cali0707 whenever you have a moment, could you take a look at this PR?