Docs - add gporca limitation for parameterized prepared statements
unsupported query is executed, Greenplum logs this notice along with the query
text:<codeblock>Feature not supported by the Pivotal Query Optimizer: UTILITY command</codeblock></p>
<p>These features are unsupported when GPORCA is enabled (the default): <ul id="ul_ndm_gyl_vp">
+ <li>Prepared statements that have parameterized values.</li>
<li>Indexed expressions (an index defined as expression based on one or more columns of
the table)</li>
<li>SP-GiST indexing method. GPORCA supports only B-tree, bitmap, GIN, and GiST indexes.
