[SPARK-10849][SQL] Adds option to the JDBC data source write for user to specify database column type for the create table

## What changes were proposed in this pull request?
Currently JDBC data source creates tables in the target database using the default type mapping, and the JDBC dialect mechanism.  If users want to specify different database data type for only some of columns, there is no option available. In scenarios where default mapping does not work, users are forced to create tables on the target database before writing. This workaround is probably not acceptable from a usability point of view. This PR is to provide a user-defined type mapping for specific columns.

The solution is to allow users to specify database column data type for the create table  as JDBC datasource option(createTableColumnTypes) on write. Data type information can be specified in the same format as table schema DDL format (e.g: `name CHAR(64), comments VARCHAR(1024)`).

All supported target database types can not be specified ,  the data types has to be valid spark sql data types also.  For example user can not specify target database  CLOB data type. This will be supported in the follow-up PR.

Example:
```Scala
df.write
.option("createTableColumnTypes", "name CHAR(64), comments VARCHAR(1024)")
.jdbc(url, "TEST.DBCOLTYPETEST", properties)
```
## How was this patch tested?
Added new test cases to the JDBCWriteSuite

Author: sureshthalamati <suresh.thalamati@gmail.com>

Closes #16209 from sureshthalamati/jdbc_custom_dbtype_option_json-spark-10849.

1 files changed, 7 insertions, 0 deletions

diff --git a/docs/sql-programming-guide.md b/docs/sql-programming-guide.md
index b077575155..7ae9847983 100644
--- a/docs/sql-programming-guide.md
+++ b/docs/sql-programming-guide.md
@@ -1223,6 +1223,13 @@ the following case-insensitive options:
      This is a JDBC writer related option. If specified, this option allows setting of database-specific table and partition options when creating a table (e.g., <code>CREATE TABLE t (name string) ENGINE=InnoDB.</code>). This option applies only to writing.
    </td>
   </tr>
+  
+  <tr>
+    <td><code>createTableColumnTypes</code></td>
+    <td>
+     The database column data types to use instead of the defaults, when creating the table. Data type information should be specified in the same format as CREATE TABLE columns syntax (e.g: <code>"name CHAR(64), comments VARCHAR(1024)")</code>. The specified types should be valid spark sql data types. This option applies only to writing.
+    </td>
+  </tr>  
 </table>
 
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