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/site-replication.go

@@ -856,12 +856,7 @@ func (c *SiteReplicationSys) MakeBucketHook(ctx context.Context, bucket string,
 	if err := errors.Unwrap(makeBucketConcErr); err != nil {
 		return err
 	}
-
-	if err := errors.Unwrap(makeRemotesConcErr); err != nil {
-		return err
-	}
-
-	return nil
+	return errors.Unwrap(makeRemotesConcErr)
 }
 
 // DeleteBucketHook - called during a regular delete bucket call when cluster