kms: add support for MinKMS and remove some unused/broken code (#19368)

This commit adds support for MinKMS. Now, there are three KMS
implementations in `internal/kms`: Builtin, MinIO KES and MinIO KMS.

Adding another KMS integration required some cleanup. In particular:
 - Various KMS APIs that haven't been and are not used have been
   removed. A lot of the code was broken anyway.
 - Metrics are now monitored by the `kms.KMS` itself. For basic
   metrics this is simpler than collecting metrics for external
   servers. In particular, each KES server returns its own metrics
   and no cluster-level view.
 - The builtin KMS now uses the same en/decryption implemented by
   MinKMS and KES. It still supports decryption of the previous
   ciphertext format. It's backwards compatible.
 - Data encryption keys now include a master key version since MinKMS
   supports multiple versions (~4 billion in total and 10000 concurrent)
   per key name.

Signed-off-by: Andreas Auernhammer <github@aead.dev>

cmd/metrics-v2.go

@@ -3970,7 +3970,7 @@ func getKMSMetrics(opts MetricsGroupOpts) *MetricsGroupV2 {
 				Help:      "Number of KMS requests that succeeded",
 				Type:      counterMetric,
 			},
-			Value: float64(metric.RequestOK),
+			Value: float64(metric.ReqOK),
 		})
 		metrics = append(metrics, MetricV2{
 			Description: MetricDescription{
@@ -3980,7 +3980,7 @@ func getKMSMetrics(opts MetricsGroupOpts) *MetricsGroupV2 {
 				Help:      "Number of KMS requests that failed due to some error. (HTTP 4xx status code)",
 				Type:      counterMetric,
 			},
-			Value: float64(metric.RequestErr),
+			Value: float64(metric.ReqErr),
 		})
 		metrics = append(metrics, MetricV2{
 			Description: MetricDescription{
@@ -3990,19 +3990,8 @@ func getKMSMetrics(opts MetricsGroupOpts) *MetricsGroupV2 {
 				Help:      "Number of KMS requests that failed due to some internal failure. (HTTP 5xx status code)",
 				Type:      counterMetric,
 			},
-			Value: float64(metric.RequestFail),
+			Value: float64(metric.ReqFail),
 		})
-		metrics = append(metrics, MetricV2{
-			Description: MetricDescription{
-				Namespace: clusterMetricNamespace,
-				Subsystem: kmsSubsystem,
-				Name:      kmsUptime,
-				Help:      "The time the KMS has been up and running in seconds.",
-				Type:      counterMetric,
-			},
-			Value: metric.UpTime.Seconds(),
-		})
-
 		return metrics
 	})
 	return mg