feat: use slog and add debuging logs

[yuvaldekel]

This PR introduces comprehensive debug logging to prom-label-proxy to make it easier to troubleshoot query enforcement, label extraction, and PromQL parsing issues. the debugging use the slog package and go by prometheus standards.
The PR Introduce two new flags log.level and log.format. Use --help to view their usage.
The PR resolve #336 issue.

[squat]

@yuvaldekel introducing structure logging sounds good to me. My main concern here is the use of the klog package specifically: we try to stay as close to upstream Prometheus tooling wherever possible, the the Prometheus project has standardized on the upstream Golang stdlib log/slog; could you switch this PR to use log/slog instead? If so, then it would be easier to merge this.

[yuvaldekel]

@yuvaldekel introducing structure logging sounds good to me. My main concern here is the use of the klog package specifically: we try to stay as close to upstream Prometheus tooling wherever possible, the the Prometheus project has standardized on the upstream Golang stdlib log/slog; could you switch this PR to use log/slog instead? If so, then it would be easier to merge this.

@squat switch to slog and added much more comprehensive debuging logs.
Hope it's good now. I whould be happy to get your review.