"insert into table select from another table" support

added insert into table support.

This feature is intended to support bulk inserts into cstore table from regular tables. Each insert statement cause creation of a new stripe. Therefore insert command is limited to "insert into <cstore_table> from select * from <another_table>' format. eg. single row inserts like insert into <cstore_table> values (....) is not supported.

Also introduced a regression test for this feature.
1. PostgreSQL uses this format of arranging function arguments, but we use a different format in cstore\_fdw. We wrap only if it will wrap to the next line.

2. Our naming conventions disallow underscore separated names.

So, we can write this as:

```
CStorePlanForeignModify(PlannerInfo *root, ModifyTable *plan,
						Index resultRelation, int subplanIndex)
```