support SELECT ... INTO OUTFILE

[zz-jason]

Feature Request

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

No

Describe the feature you'd like:

From MySQL documentation 13.2.10.1 SELECT ... INTO OUTFILE Syntax:

SELECT ... INTO OUTFILE writes the selected rows to a file. Column and line terminators can be specified to produce a specific output format.

It helps us to store the query result in a CSV form.

After this issue pingcap/parser#722, you have to implement a SelectIntoExec like the ExplainExec to let TiDB support this new syntax.
Describe alternatives you've considered:

No

Teachability, Documentation, Adoption, Migration Strategy:

No