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>

go.sum

@@ -438,6 +438,8 @@ github.com/minio/highwayhash v1.0.2 h1:Aak5U0nElisjDCfPSG79Tgzkn2gl66NxOMspRrKnA
 github.com/minio/highwayhash v1.0.2/go.mod h1:BQskDq+xkJ12lmlUUi7U0M5Swg3EWR+dLTk+kldvVxY=
 github.com/minio/kms-go/kes v0.3.0 h1:SU8VGVM/Hk9w1OiSby3OatkcojooUqIdDHl6dtM6NkY=
 github.com/minio/kms-go/kes v0.3.0/go.mod h1:w6DeVT878qEOU3nUrYVy1WOT5H1Ig9hbDIh698NYJKY=
+github.com/minio/kms-go/kms v0.4.0 h1:cLPZceEp+05xHotVBaeFJrgL7JcXM4lBy6PU0idkE7I=
+github.com/minio/kms-go/kms v0.4.0/go.mod h1:q12CehiIy2qgBnDKq6Q7wmPi2PHSyRVug5DKp0HAVeE=
 github.com/minio/madmin-go/v3 v3.0.51 h1:brGOvDP8KvoHb/bdzCHUPFCbTtrN8o507uPHZpyuinM=
 github.com/minio/madmin-go/v3 v3.0.51/go.mod h1:IFAwr0XMrdsLovxAdCcuq/eoL4nRuMVQQv0iubJANQw=
 github.com/minio/mc v0.0.0-20240430174448-dcb911bed9d5 h1:VDXLzvY0Jxk4lzIntGXZuw0VH7S1JgQBmjWGkz7xphU=