fix: populate OTel resource attributes from env var

[adamflorence-nullify]

Description

resource.New() in configureOTel() was missing resource.WithFromEnv(), so resource attributes set via OTEL_RESOURCE_ATTRIBUTES (including nul.deployment_id and deployment.environment) were never attached to the OTel resource.

This meant they appeared on target_info (resource metadata) but not on any application metric (nul_pipeline_event_total, nul_scan_duration_seconds, etc.), making per-customer metric queries impossible.

Impact: Once deployed, all nul_* metrics will gain nul_deployment_id as a label, enabling per-customer alerting (e.g. pipeline volume drop/spike alerts) and dashboarding.

Test Plan

• go build ./... passes
• go test ./pkg/logger/... -short passes
• After deploy to one service, verify nul_deployment_id appears on application metrics in Prometheus (not just target_info)
• Verify with: group by (nul_deployment_id) (nul_pipeline_event_total{deployment_environment="prod", nul_deployment_id!=""})

Checklist

• I have performed a self-review of my own code
• I have checked for redundant or commented out code
• I have made corresponding changes to the documentation
• I have added any appropriate tests

[dnjg]

deployment.environment was already being populated for the metrics from that env var, so i'm not sure this is quite right. is the distinction that we need that setting to enable it for custom attributes as opposed to standard otel ones?