This is the next step in removing the top level sql directory.
I named the directory `sql-cli` instead of `cli` because that puts it at
the maven coordinates `org.elasticsearch.plugin:sql-cli` instead of
`org.elasticsearch.plugin:cli`.
Relates to elastic/x-pack-elasticsearch#3363
Original commit: elastic/x-pack-elasticsearch@d41a57a136
This moves SQL's server project into `plugin:sql` without modifying how the integration is performed. I know that it is not correct with regards to the x-pack modularization but I think it is a good first step.
Original commit: elastic/x-pack-elasticsearch@2f40d02e4d