Fix PostgreSQL insert to properly extract table name from multiline string SQL.

Previously, executing an insert SQL in PostgreSQL with a command like this:

    insert into articles(
      number)
    values(
      5152
    )

would not work because the adapter was unable to extract the correct articles table name.
Merge pull request #13395 from kuldeepaggarwal/postgres-table-ref-regex

modified regex for finding table_name from a multiline sql query in postgresql