docs: gptransfer - add sha-256 option for --validate option (#3362)

* docs: gptransfer - add sha-256 option for --validate option

* update based on review comments.
--changed option value from sha-256 to sha256
--move GPDB 4.3.x information to the notes section.

* Update/clarify based on review comments.
--clarified GPDB 4.3.x pgcrypto information.
--clarified --validate options.

* docs: minor update

* Conditionalizing the pivotal reference

* Extending conditionalized phrase to cover 4.3 stuff.

gpdb-doc/dita/utility_guide/admin_utilities/gptransfer.xml

@@ -204,6 +204,14 @@
                     utility uses a different configuration of named pipes and
                         <codeph>gpfdist</codeph> instances in the two situations. </p>
             </sectiondiv>
+            <sectiondiv><b>Validating Table Data with SHA-256</b>
+                <p>Validating table data with SHA-256 (specifying the option
+                        <codeph>--validate=sha256</codeph>) requires the Greenplum Database pgcrypto
+                    extension. <ph otherprops="pivotal">The extension is included with Pivotal Greenplum 5.x. When copying
+                    data from a supported Pivotal Greenplum 4.3.x system, the extension package must
+                    be installed on the 4.3.x system. You do not need to run
+                        <codeph>pgcrypto.sql</codeph> to install the pgcrypto functions in a
+                    Greenplum 4.3.x database.</ph></p></sectiondiv>
         </section>
         <section id="section6">
             <title>Options</title>
@@ -725,12 +733,22 @@ sdw4,192.0.2.4</codeblock>
                 </plentry>
                 <plentry>
                     <pt>--validate=<varname>type</varname></pt>
-                    <pd>Perform data validation on table data. These are the supported types of
-                        validation.</pd>
+                    <pd>Perform data validation on table data. The default is no validation. These
+                        are the supported types of validation.</pd>
                     <pd><codeph>count</codeph> - Specify this value to compare row counts between
                         source and destination table data.</pd>
-                    <pd><codeph>MD5</codeph> - Specify this value to compare MD5 values between
+                    <pd><codeph>md5</codeph> - Specify this value to compare MD5 values between
                         source and destination table data. </pd>
+                    <pd><codeph>sha256</codeph> - Specify this value to compare SHA-256 values
+                        between source and destination table data. For more information about using
+                            <codeph>sha256</codeph>, see <xref href="#topic1/section4" format="dita"
+                            >Notes</xref>.</pd>
+                    <pd>
+                        <note>On a Greenplum Database system with FIPS enabled, the option
+                                <codeph>md5</codeph> is not supported. Use the
+                                <codeph>count</codeph> or <codeph>sha256</codeph> option to validate
+                            table data. </note>
+                    </pd>
                     <pd>If validation for a table fails, <codeph>gptransfer</codeph> displays the
                         name of the table and writes the file name to the text file
                             <codeph>failed_migrated_tables_</codeph><varname>yyyymmdd_hhmmss</varname><codeph>.txt</codeph>.