Support databases inside ManticoreSearch

[AbstractiveNord]

Is your feature request related to a problem? Please describe. Mostly new users of ManticoreSearch have problems with CRUD operations about databases. It's unexpected to have CREATE (and others) DATABASES query to work good, but doing nothing. No way to separate different namespaces of tables.

Describe the solution you'd like Implement CRUD operations for DATABASE and remove stub queries.

Additional context Stub queries was made as bypass for some clients applications, database IDEs.

[sanikolaev]

Things to think through and notes after call with Alexey:

• default database

mysql> show tables;
ERROR 1046 (3D000): No database selected

• dist of locals:

create table dist type='distributed' local='db.tbl' local='db2.tbl2'

• database name is not a part of the protocol, e.g. when you run status on the client it doesn't take the database name from the protocol, it does select database() etc.

• the way to migrate to the db ON mode.

• how this should work together with replication clusters

[sanikolaev]

Alexey suggests to add a new setting like databases_dir in addition to data_dir.