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/object_api_suite_test.go

@@ -521,11 +521,11 @@ func enableCompression(t *testing.T, encrypt bool) {
 	globalCompressConfigMu.Unlock()
 	if encrypt {
 		globalAutoEncryption = encrypt
-		var err error
-		GlobalKMS, err = kms.Parse("my-minio-key:5lF+0pJM0OWwlQrvK2S/I7W9mO4a6rJJI7wzj7v09cw=")
+		KMS, err := kms.ParseSecretKey("my-minio-key:5lF+0pJM0OWwlQrvK2S/I7W9mO4a6rJJI7wzj7v09cw=")
 		if err != nil {
 			t.Fatal(err)
 		}
+		GlobalKMS = KMS
 	}
 }
 
@@ -536,11 +536,11 @@ func enableEncryption(t *testing.T) {
 	globalCompressConfigMu.Unlock()
 
 	globalAutoEncryption = true
-	var err error
-	GlobalKMS, err = kms.Parse("my-minio-key:5lF+0pJM0OWwlQrvK2S/I7W9mO4a6rJJI7wzj7v09cw=")
+	KMS, err := kms.ParseSecretKey("my-minio-key:5lF+0pJM0OWwlQrvK2S/I7W9mO4a6rJJI7wzj7v09cw=")
 	if err != nil {
 		t.Fatal(err)
 	}
+	GlobalKMS = KMS
 }
 
 func resetCompressEncryption() {