Interactive setup should validate configuration entries using original schema objects

[azasypkin]

Summary

Currently interactive setup can write the following configuration entries directly to the disk:

• elasticsearch.hosts
• elasticsearch.serviceAccountToken
• elasticsearch.password
• elasticsearch.username
• elasticsearch.ssl.certificateAuthorities

We do our best to make sure we write valid values, but there is no guarantee our validation logic will function as expected in case original configuration schema changes. Ideally we should validate all config entries we write to the disk using original schema objects that Kibana uses to validate those entries itself. This way our validation logic will always be up-to-date.

Currently we deal only with the config owned by the Core, but there is a chance we'll also need to support plugin-specific config (e.g. encryption keys, authentication providers etc.). The solution should account for that as well.

[elasticmachine]

Pinging @elastic/kibana-security (Team:Security)