Prototype to secure secret keys

[radcortez]

This is a prototype to support secret keys.

• We use property expressions to represent a secret key value in the format `${provider_name:provider_custom_representation}
  • For instance a keystore would use ${file-vault:keystore_name/alias}
  • The Jasypt provider would use ${jasypt:ENC(secret)}
• Backed by an interceptor to process each provider. Such interceptors run before the default expressions, so it doesn't clash.

[radcortez]

/cc @dmlloyd @sberyozkin

[radcortez]

Replaced by https://github.com/smallrye/smallrye-config/pull/833.