Implement 'openssl' style for supporting different providers of key/trust store password

Following the 'openssl' approach, we will add zookeeper.ssl.keyStore.passwordProvider which defaults to pass and can be set to file or env. ZK then interprets the zookeeper.ssl.keyStore.password according to the zookeeper.ssl.keyStore.passwordProvider

Details can be found in.
https://github.com/apache/zookeeper/pull/1773#discussion_r728281819