Support column_list for redshift_load operator

[toru-takahashi]

Looks like column_list option hasn't not implemented yet even though the doc shows it.

Because, I found copy statement is build by the following syntax.

digdag/digdag-standards/src/main/java/io/digdag/standards/operator/redshift/RedshiftConnection.java

Lines 127 to 134 in d1de1e0

	String buildCopyStatement(CopyConfig copyConfig, boolean maskCredentials)
	{
	StringBuilder sb = new StringBuilder();
	sb.append(
	String.format("COPY %s FROM '%s'\n",
	escapeIdent(copyConfig.table),
	escapeParam(copyConfig.from)));

       sb.append(
                String.format("COPY %s FROM '%s'\n",
                        escapeIdent(copyConfig.table),
                        escapeParam(copyConfig.from)));

But, The expected syntax is COPY tablename (column1 [,column2, ...])

So, copy_list option is allowed by the following but the logic hasn’t been implemented yet.

digdag/digdag-standards/src/main/java/io/digdag/standards/operator/redshift/RedshiftLoadOperatorFactory.java

Line 158 in d1de1e0

copyConfig.columnList = config.getOptional("column_list", String.class);

It’s a documentation bug. What we need to do is…

• Remove column_list option from the doc for now
• Support column_list option for redshift_load operator