Add certificates_checked_total metric

[dllegru]

Summary

• Add certificator_certificates_checked_total{domain, status} counter metric
• Status labels: valid (no renewal needed), renewed (successfully renewed), failure (renewal failed)
• Ensures every batch run produces metrics regardless of whether renewals occur

Test plan

• Deploy to staging and trigger batch job
• Verify certificator_certificates_checked_total appears in VictoriaMetrics
• Confirm status label values are correct for each domain

[github-actions]

Code Coverage Report

Total Coverage: total: (statements) 24.7%

Coverage by function

github.com/vinted/certificator/cmd/certificatee/helpers.go:9:		createHAProxyClients	0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:21:		main			0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:72:		maybeUpdateCertificates	0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:88:		processHAProxyEndpoint	0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:152:		shouldUpdateCertificate	0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:176:		updateCertificate	0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:198:		buildPEMBundle		0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:224:		endsWith		0.0%
github.com/vinted/certificator/cmd/certificator/main.go:18:		main			0.0%
github.com/vinted/certificator/pkg/acme/acme.go:27:			GetEmail		0.0%
github.com/vinted/certificator/pkg/acme/acme.go:32:			GetRegistration		0.0%
github.com/vinted/certificator/pkg/acme/acme.go:37:			GetPrivateKey		0.0%
github.com/vinted/certificator/pkg/acme/acme.go:42:			NewClient		0.0%
github.com/vinted/certificator/pkg/acme/acme.go:61:			setupClient		0.0%
github.com/vinted/certificator/pkg/acme/acme.go:80:			setupAccount		0.0%
github.com/vinted/certificator/pkg/acme/acme.go:118:			newAccount		0.0%
github.com/vinted/certificator/pkg/acme/acme.go:130:			getAccountKey		0.0%
github.com/vinted/certificator/pkg/acme/acme.go:159:			registerAccount		0.0%
github.com/vinted/certificator/pkg/acme/acme.go:177:			recoverAccount		0.0%
github.com/vinted/certificator/pkg/acme/acme.go:211:			saveAccount		0.0%
github.com/vinted/certificator/pkg/acme/acme.go:221:			saveKey			0.0%
github.com/vinted/certificator/pkg/certificate/certificate.go:18:	ObtainCertificate	0.0%
github.com/vinted/certificator/pkg/certificate/certificate.go:50:	GetCertificate		0.0%
github.com/vinted/certificator/pkg/certificate/certificate.go:68:	NeedsReissuing		0.0%
github.com/vinted/certificator/pkg/certificate/certificate.go:96:	arraysEqual		0.0%
github.com/vinted/certificator/pkg/certificate/certificate.go:110:	arrayContains		0.0%
github.com/vinted/certificator/pkg/certificate/certificate.go:119:	VaultCertLocation	0.0%
github.com/vinted/certificator/pkg/certificate/certificate.go:123:	storeCertificateInVault	0.0%
github.com/vinted/certificator/pkg/certmetrics/metrics.go:65:		StartMetricsServer	0.0%
github.com/vinted/certificator/pkg/certmetrics/metrics.go:85:		PushMetrics		0.0%
github.com/vinted/certificator/pkg/config/config.go:72:			LoadConfig		0.0%
github.com/vinted/certificator/pkg/haproxy/client.go:50:		NewClient		100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:85:		NewClients		92.3%
github.com/vinted/certificator/pkg/haproxy/client.go:110:		Endpoint		100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:115:		doRequest		88.9%
github.com/vinted/certificator/pkg/haproxy/client.go:149:		ListCertificates	100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:163:		ListCertificateRefs	85.7%
github.com/vinted/certificator/pkg/haproxy/client.go:201:		UpdateCertificate	80.0%
github.com/vinted/certificator/pkg/haproxy/client.go:237:		CreateCertificate	78.9%
github.com/vinted/certificator/pkg/haproxy/client.go:272:		DeleteCertificate	100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:291:		ExtractDomainFromPath	100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:309:		IsExpiring		100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:320:		NormalizeSerial		100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:330:		Error			100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:334:		Info			0.0%
github.com/vinted/certificator/pkg/haproxy/client.go:338:		Debug			100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:342:		Warn			0.0%
github.com/vinted/certificator/pkg/haproxy/client.go:347:		toLogrusFields		85.7%
github.com/vinted/certificator/pkg/vault/vault.go:18:			NewVaultClient		0.0%
github.com/vinted/certificator/pkg/vault/vault.go:27:			KVWrite			0.0%
github.com/vinted/certificator/pkg/vault/vault.go:41:			KVRead			0.0%
github.com/vinted/certificator/pkg/vault/vault.go:62:			vaultFullPath		0.0%
total:									(statements)		24.7%