feat(operator): Implement OptimizationJob reconciler loop

[Swaraj-do]

What this PR does / why we need it

This PR implements the OptimizationJobReconciler controller in pkg/controller/optimizationjob_controller.go to orchestrate hyperparameter tuning trial TrainJobs per KEP-3562 (https://github.com/kubeflow/trainer/blob/master/proposals/2605-optimization-job-crd/README.md).

Key Features Implemented

• Controller Reconciler: Implemented OptimizationJobReconciler with ctrl.NewControllerManagedBy(mgr) watching OptimizationJob and owning child TrainJobs.
• Trial Orchestration: Dynamically provisions trial TrainJobs from spec.trainJobTemplate.
• Parameter Sampling & Injection: Samples parameter values across Categorical, Uniform, and LogUniform search spaces and injects them as environment variables (KUBEFLOW_TRAINER_OPT_) into trainJob.spec.trainer.env and metadata annotations.
• Concurrency & Limits: Enforces parallelTrials concurrency limits and total numTrials limits.
• Status & Result Recording: Initializes .status.conditions (Created, Complete, Failed) and records highest-performing trial parameters in .status.result.
• Controller Registration: Registered NewOptimizationJobReconciler in SetupControllers (pkg/controller/setup.go).
• Unit Test Suite: Added unit tests in pkg/controller/optimizationjob_controller_test.go verifying reconciler status initialization, trial creation, env var injection, and trial completion.

Which issue(s) this PR fixes

Fixes #3877

Checklist

• Title follows conventional commit guidelines (feat(controller): ...)
• Code complies with project style and guidelines
• Unit tests added and passing cleanly (go test ./pkg/controller/...)
• DCO Signed-off

[google-oss-prow]

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