Add support to parse message elements in JDBCAppender column configuration

[gaurav deshpande <ga...@gmail.com>]

Hi log4j2 developers,

I have created custom-message implementing 'message' interface.

I have also created JDBCAppender which writes values from above message to
database table.

But how do I get the value from custom message and store it into databse?

I've tried pattern attribute in column tag in jdbcappender but thats not
working.

Input: custom message
Output: store it into database table

If not available, can you please add support to parse message elements in
JDBCAppender column configuration

Thanks,
Gaurav