Minor Improvements: Log Level and Metrics Documentation

[piceri]

This change contains the following minor changes:

• Enable controlling log level via env var
• Renamed deptracker_post_record_no_attestation to deptracker_post_record_unknown_artifact
• Add documentation for deptracker_post_record_unknown_artifact_cache_hit to README

[Copilot]

Pull request overview

This PR makes small operational and observability updates to deployment-tracker by adding env-configurable logging and adjusting Prometheus metric naming/documentation around unknown artifacts and caching.

Changes:

• Add LOG_LEVEL environment variable support for controlling slog handler level.
• Rename the “no attestation” post counter metric to “unknown artifact” and update code/tests to use the new name.
• Document the unknown-artifact cache hit metric in the README.

Show a summary per file

File	Description
pkg/dtmetrics/prom.go	Renames the exported counter and Prometheus metric name for unknown-artifact post outcomes.
pkg/deploymentrecord/client.go	Updates the 404-path metric increment to use the renamed counter.
pkg/deploymentrecord/client_test.go	Updates metric assertions and test struct fields to match the renamed counter.
cmd/deployment-tracker/main.go	Adds LOG_LEVEL parsing and configures slog handler level from env var.
README.md	Documents LOG_LEVEL and updates/extends metrics documentation for unknown-artifact behavior and cache hits.

Copilot's findings

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Comments suppressed due to low confidence (1)

pkg/deploymentrecord/client.go:276

• The 404 branch currently treats any 404 as a NoArtifactError and increments the ...unknown_artifact metric. That contradicts the NoArtifactError type comment/tests implying it’s specifically for 404s whose body indicates "no artifacts found", and it risks caching/suppressing posts for other 404 causes (bad org/base URL, endpoint changes, etc.). Consider validating the response body/message before returning NoArtifactError (and only then incrementing the unknown-artifact metric); otherwise treat other 404s as client errors.

		case resp.StatusCode == 404:
			// No artifact found - do not retry
			dtmetrics.PostDeploymentRecordUnknownArtifact.Inc()
			slog.Debug("no artifact attestation found, no record created",
				"attempt", attempt,
				"status_code", resp.StatusCode,
				"container_name", record.Name,
				"resp_msg", string(respBody),
				"digest", record.Digest,
			)
			return &NoArtifactError{err: fmt.Errorf("no attestation found for %s", record.Digest)}

• Files reviewed: 5/5 changed files
• Comments generated: 4