Add missing documentation for input.flowfile.uuid attribute of ExecuteSQL processors

As part of NIFI-6271, a "input.flowfile.uuid" attribute was added to the ExecuteSQL processors, and will be populated (if there was an incoming flow file) with the incoming flow file's UUID. This can be used with the "incremental commit" feature of ExecuteSQL and ExecuteSQLRecord, namely when Output Batch Size is > 0.

However the attribute was not added to the documentation for these processors under NIFI-6271 so this Jira proposes to add the additional doc.