doc: Add additional index entries for progress reporting views.

In the docs, the index entries for progress reporting views link to
the "Viewing Statistics" section, but previously they did not link to
the dedicated section (e.g., "ANALYZE Progress Reporting") for
each view. This was inconvenient when finding the section describing
the detailed information about each view, from the index.
This commit adds additional index entries linking to those dedicated
sections.

Author: Fujii Masao
Reviewed-by: Shinya Kato
Discussion: https://postgr.es/m/e49c2768-65d2-188a-5424-270fa29ccc84@oss.nttdata.com

doc/src/sgml/monitoring.sgml

@@ -5229,6 +5229,10 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
  <sect2 id="analyze-progress-reporting">
   <title>ANALYZE Progress Reporting</title>
 
+  <indexterm>
+   <primary>pg_stat_progress_analyze</primary>
+  </indexterm>
+
   <para>
    Whenever <command>ANALYZE</command> is running, the
    <structname>pg_stat_progress_analyze</structname> view will contain a
@@ -5442,6 +5446,10 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
  <sect2 id="create-index-progress-reporting">
   <title>CREATE INDEX Progress Reporting</title>
 
+  <indexterm>
+   <primary>pg_stat_progress_create_index</primary>
+  </indexterm>
+
   <para>
    Whenever <command>CREATE INDEX</command> or <command>REINDEX</command> is running, the
    <structname>pg_stat_progress_create_index</structname> view will contain
@@ -5738,6 +5746,10 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
  <sect2 id="vacuum-progress-reporting">
   <title>VACUUM Progress Reporting</title>
 
+  <indexterm>
+   <primary>pg_stat_progress_vacuum</primary>
+  </indexterm>
+
   <para>
    Whenever <command>VACUUM</command> is running, the
    <structname>pg_stat_progress_vacuum</structname> view will contain
@@ -5964,6 +5976,10 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
  <sect2 id="cluster-progress-reporting">
   <title>CLUSTER Progress Reporting</title>
 
+  <indexterm>
+   <primary>pg_stat_progress_cluster</primary>
+  </indexterm>
+
   <para>
    Whenever <command>CLUSTER</command> or <command>VACUUM FULL</command> is
    running, the <structname>pg_stat_progress_cluster</structname> view will
@@ -6182,6 +6198,10 @@ SELECT pg_stat_get_backend_pid(s.backendid) AS pid,
  <sect2 id="basebackup-progress-reporting">
   <title>Base Backup Progress Reporting</title>
 
+  <indexterm>
+   <primary>pg_stat_progress_basebackup</primary>
+  </indexterm>
+
   <para>
    Whenever an application like <application>pg_basebackup</application>
    is taking a base backup, the