Design syntax for using Lightning from SQL

[kennytm]

Feature Request

Is your feature request related to a problem? Please describe:

Integrating Lightning into TiDB requires an SQL syntax.

Describe the feature you'd like:

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Optimization:

[kennytm]

Referring to pingcap/parser#746, we will support use the syntax like this:

IMPORT DATABASE * FROM 'file:///data/sql_dump';
IMPORT TABLE db1.tbl1, db1.tbl2 FROM 'file:///data/csv_dump';

-- lightning options
IMPORT DATABASE * FROM 'file:///data/csv_dump' 
    CHECKSUM = 0
    ANALYZE = 0
    CHECKPOINT = 0;

-- view tasks
SHOW IMPORT;
SHOW IMPORT LIKE '%csv%';
SHOW IMPORT WHERE `Progress` = 'Wait';

The main issue is to sort out the list of options to be exposed.