This commit adds support for encrypted KES
client private keys.
Now, it is possible to encrypt the KES client
private key (`MINIO_KMS_KES_KEY_FILE`) with
a password.
For example, KES CLI already supports the
creation of encrypted private keys:
```
kes identity new --encrypt --key client.key --cert client.crt MinIO
```
To decrypt an encrypted private key, the password
needs to be provided:
```
MINIO_KMS_KES_KEY_PASSWORD=<password>
```
Signed-off-by: Andreas Auernhammer <hi@aead.dev>
e955aa7f2a