feat: add certificatee health endpoint

[ananthb]

Summary

• add a real /health endpoint alongside /metrics
• make certificatee health depend on Vault access, HAProxy Data Plane API reachability, and a recent successful sync
• expose the same endpoint shape from certificator with a Vault token check and add handler tests

Testing

• env GOCACHE=/tmp/go-build-certificator go test ./pkg/certmetrics ./cmd/certificatee ./cmd/certificator

[github-actions]

Code Coverage Report

Total Coverage: total: (statements) 27.1%

Coverage by function

github.com/vinted/certificator/cmd/certificatee/health.go:21:		Mark				0.0%
github.com/vinted/certificator/cmd/certificatee/health.go:35:		Check				0.0%
github.com/vinted/certificator/cmd/certificatee/health.go:56:		newCertificateeHealthChecker	0.0%
github.com/vinted/certificator/cmd/certificatee/helpers.go:9:		createHAProxyClients		0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:22:		main				0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:80:		maybeUpdateCertificates		0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:96:		processHAProxyEndpoint		0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:180:		shouldUpdateCertificate		0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:218:		updateCertificate		0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:240:		buildPEMBundle			0.0%
github.com/vinted/certificator/cmd/certificatee/main.go:266:		endsWith			0.0%
github.com/vinted/certificator/cmd/certificator/main.go:20:		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:76:		StartMetricsServer		0.0%
github.com/vinted/certificator/pkg/certmetrics/metrics.go:101:		newHandler			100.0%
github.com/vinted/certificator/pkg/certmetrics/metrics.go:125:		PushMetrics			0.0%
github.com/vinted/certificator/pkg/config/config.go:73:			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:133:		parseAPITime			66.7%
github.com/vinted/certificator/pkg/haproxy/client.go:146:		getConfigVersion		66.7%
github.com/vinted/certificator/pkg/haproxy/client.go:211:		ListCertificates		100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:225:		ListCertificateRefs		85.7%
github.com/vinted/certificator/pkg/haproxy/client.go:264:		GetCertificateDetail		68.4%
github.com/vinted/certificator/pkg/haproxy/client.go:305:		UpdateCertificate		85.7%
github.com/vinted/certificator/pkg/haproxy/client.go:329:		CreateCertificate		78.3%
github.com/vinted/certificator/pkg/haproxy/client.go:370:		DeleteCertificate		92.9%
github.com/vinted/certificator/pkg/haproxy/client.go:394:		ExtractDomainFromPath		100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:414:		NormalizeDomainForVault		0.0%
github.com/vinted/certificator/pkg/haproxy/client.go:422:		IsExpiring			100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:433:		NormalizeSerial			100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:456:		Error				100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:460:		Info				0.0%
github.com/vinted/certificator/pkg/haproxy/client.go:464:		Debug				100.0%
github.com/vinted/certificator/pkg/haproxy/client.go:468:		Warn				0.0%
github.com/vinted/certificator/pkg/haproxy/client.go:473:		toLogrusFields			85.7%
github.com/vinted/certificator/pkg/vault/vault.go:18:			NewVaultClient			0.0%
github.com/vinted/certificator/pkg/vault/vault.go:27:			TokenLookupSelf			0.0%
github.com/vinted/certificator/pkg/vault/vault.go:39:			KVWrite				0.0%
github.com/vinted/certificator/pkg/vault/vault.go:53:			KVRead				0.0%
github.com/vinted/certificator/pkg/vault/vault.go:74:			vaultFullPath			0.0%
total:									(statements)			27.1%