Added unit test for pkg/cluster/node_reconciler.go file

[Alokzh]

Description

This PR introduces a comprehensive unit test suite for the node_reconciler.go file within the pkg/cluster package. These tests ensure that the logic for discovering and updating the list of gateway node IPs is reliable & handles various edge cases correctly

How Has This Been Tested?

The new functionality has been validated through local unit testing

go test -v ./pkg/cluster/...
go test -v ./pkg/cluster/... -cover

Overall Coverage Increase: This PR increases the overall coverage by 0.7%

Checklist:

• The title of the PR states what changed and the related issues number (used for the release note).
• Does this PR requires documentation updates?
• I've updated documentation as required by this PR.
• I have ran go fmt
• I have updated the helm chart as required by this PR.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have tested it for all user roles.
• I have added all the required unit test cases.
• I have verified the E2E test cases with new code changes.
• I have added all the required E2E test cases.

Does this PR introduce a breaking change?