Generate HTML coverage report after running unit tests

[shadowinlife]

Purpose of this PR

This pull request adds a new Makefile target to make it easier to generate and view test coverage reports after running unit tests.

Testing and coverage improvements:

• Added a .PHONY target named coverage to the Makefile, which generates an HTML coverage report (cover.html) from the output of unit tests, making it easier to visualize code coverage.

make help

Usage:
  make <target>

General
  help                            Display this help.
  version                         Print version information.

Development
  manifests                       Generate CustomResourceDefinition, RBAC and WebhookConfiguration manifests.
  generate                        Generate code containing DeepCopy, DeepCopyInto, and DeepCopyObject method implementations.
  update-crd                      Update CRD files in the Helm chart.
  verify-codegen                  Install code-generator commands and verify changes
  go-clean                        Clean up caches and output.
  go-fmt                          Run go fmt against code.
  go-vet                          Run go vet against code.
  go-lint                         Run golangci-lint linter.
  go-lint-fix                     Run golangci-lint linter and perform fixes.
  unit-test                       Run unit tests.
  coverage                        Generate HTML coverage report in cover.html.
  e2e-test                        Run the e2e tests against a Kind k8s instance that is spun up.

HTML Results as

Change Category

• Bugfix (non-breaking change which fixes an issue)
• Feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that could affect existing functionality)
• Documentation update

Rationale

Checklist

• I have conducted a self-review of my own code.
• I have updated documentation accordingly.
• I have added tests that prove my changes are effective or that my feature works.
• Existing unit tests pass locally with my changes.

Additional Notes

[shadowinlife]

@ChenYi015 this PR is ready for review. thanks

[ChenYi015]

/approve

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ChenYi015

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