Migrate Keystore to New Platform

[tylersmalley]

The keystore settings either need exposed by a new plugin in the new platform, or added to core. Currently, these settings are being injected into the Hapi.

The libraries for this are located at https://github.com/elastic/kibana/tree/master/src/legacy/server/keystore

@joshdover do you have a preference for if this should be a new plugin or exposed vai core?

• Remove utils/{question,prompt}

[elasticmachine]

Pinging @elastic/kibana-operations (Team:Operations)

[joshdover]

This seems wrong, but the only usages I find are in CLI tools. I'm not familiar with what we use the keystore for in Kibana, are there plugins using this API?

If not, could we not move this to somewhere in src/cli or src/cli_keystore?