All TLS/SSL certificate provider should accommodate encrypted key

Is your feature request related to a problem? Please describe.
Currently we have the following certificate providers on source plugin (server) and peer forwarder (client)

• local file
• s3
• ACM
  where only ACM supports encrypted key file with passphrase.

Describe the solution you'd like
We should support encrypted key with passphrase for all certificate provider since key file encryption standard is generic.

Approach:
Since Armeria server provides the API to configure TLS with encrypted key and passphrase, we only need to modify the Certificate model to accommodate encrypted key and passphrase.

Describe alternatives you've considered (Optional)
Alternatively, we could refactor the decrypt method existing in ACM provider into a common SSL utility method for reusage. This will work with servers that happen not to support encrypted private key. We do not have such use case so far.

Additional context
Add any other context or screenshots about the feature request here.

Start with the Certificate model and the provider implementations for local files, S3, and ACM, then read the decrypt method in ACMCertificateProvider.java. Trace how certificates are passed to the source plugin and peer forwarder, and verify that encrypted private keys and passphrases work for every provider.