doc: Improve description of new random(min, max) functions.

Mention that the new variants of random(min, max) are affected by
setseed(), like the original functions.

Reported-by: Marcos Pegoraro <marcos@f10.com.br>
Discussion: https://postgr.es/m/CAB-JLwb1=drA3Le6uZXDBi_tCpeS1qm6XQU7dKwac_x91Z4qDg@mail.gmail.com

doc/src/sgml/func/func-datetime.sgml

@@ -948,6 +948,12 @@
         Returns a random value in the range
         <parameter>min</parameter> &lt;= x &lt;= <parameter>max</parameter>.
        </para>
+       <para>
+        Note that these functions use the same pseudo-random number generator
+        as the functions listed in <xref linkend="functions-math-random-table"/>,
+        and respond in the same way to calling
+        <link linkend="function-setseed"><function>setseed()</function></link>.
+       </para>
        <para>
         <literal>random('1979-02-08'::date,'2025-07-03'::date)</literal>
         <returnvalue>1983-04-21</returnvalue>

doc/src/sgml/func/func-math.sgml

@@ -1130,7 +1130,7 @@
 
       <row>
        <entry role="func_table_entry"><para role="func_signature">
-        <indexterm>
+        <indexterm id="function-setseed">
          <primary>setseed</primary>
         </indexterm>
         <function>setseed</function> ( <type>double precision</type> )