Add 'gator benchmark' command for policy performance evaluation

[JaydipGabani]

Describe the solution you'd like
A new gator subcommand to benchmark policy performance, similar to the benchmarking in Gatekeeper policy_benchmark_test.go. The goal is to provide policy authors and Gatekeeper users a way to measure the performance of their policies (constraints/templates), using a tool directly in the gator CLI.

Key requirements:

• Allow selection of constraints, templates, and resources to benchmark
• Ability to configure the number/scale of constraints and resources evaluated (similar to existing load array: [5, 10, 50, ...])
• Flexible output: support plain text and JSON, suitable for CI or local use
• Captures metrics such as validation time, memory usage, constraint evaluation counts, and potential other policy-related metrics

Anything else you would like to add:

• Should be easily scriptable for local and CI workflows
• Ideally produces Go benchmark-compatible output
• Reference implementation: policy_benchmark_test.go
• If possible, allow targeting multiple templates/constraints/types of resources
• Useful for regression detection in policy performance

Environment:

• Gatekeeper version: [please fill]
• Kubernetes version: (use kubectl version)