Doc: Update ulinks to RFC documents to avoid redirect

The tools.ietf.org site has been decommissioned and replaced by a
number of sites serving various purposes.  Links to RFCs and BCPs
are now 301 redirected to their new respective IETF sites.  Since
this serves no purpose and only adds network overhead, update our
links to the new locations.

Backpatch to all supported versions.

Discussion: https://postgr.es/m/3C1CEA99-FCED-447D-9858-5A579B4C6687@yesql.se
Backpatch-through: v12

doc/src/sgml/charset.sgml

@@ -834,7 +834,7 @@ CREATE COLLATION german (provider = libc, locale = 'de_DE');
 
     See <ulink url="http://unicode.org/reports/tr35/tr35-collation.html">Unicode
     Technical Standard #35</ulink>
-    and <ulink url="https://tools.ietf.org/html/bcp47">BCP 47</ulink> for
+    and <ulink url="https://www.rfc-editor.org/info/bcp47">BCP 47</ulink> for
     details.  The list of possible collation types (<literal>co</literal>
     subtag) can be found in
     the <ulink url="https://github.com/unicode-org/cldr/blob/master/common/bcp47/collation.xml">CLDR

doc/src/sgml/client-auth.sgml

@@ -1079,7 +1079,7 @@ omicron         bryanh                  guest1
       <para>
        The method <literal>scram-sha-256</literal> performs SCRAM-SHA-256
        authentication, as described in
-       <ulink url="https://tools.ietf.org/html/rfc7677">RFC 7677</ulink>.  It
+       <ulink url="https://datatracker.ietf.org/doc/html/rfc7677">RFC 7677</ulink>.  It
        is a challenge-response scheme that prevents password sniffing on
        untrusted connections and supports storing passwords on the server in a
        cryptographically hashed form that is thought to be secure.
@@ -1191,7 +1191,7 @@ omicron         bryanh                  guest1
    <para>
     <productname>GSSAPI</productname> is an industry-standard protocol
     for secure authentication defined in
-    <ulink url="https://tools.ietf.org/html/rfc2743">RFC 2743</ulink>.
+    <ulink url="https://datatracker.ietf.org/doc/html/rfc2743">RFC 2743</ulink>.
     <productname>PostgreSQL</productname>
     supports <productname>GSSAPI</productname> for authentication,
     communications encryption, or both.

doc/src/sgml/json.sgml

@@ -13,7 +13,7 @@
 
  <para>
   JSON data types are for storing JSON (JavaScript Object Notation)
-  data, as specified in <ulink url="https://tools.ietf.org/html/rfc7159">RFC
+  data, as specified in <ulink url="https://datatracker.ietf.org/doc/html/rfc7159">RFC
   7159</ulink>. Such data can also be stored as <type>text</type>, but
   the JSON data types have the advantage of enforcing that each
   stored value is valid according to the JSON rules.  There are also

doc/src/sgml/libpq.sgml

@@ -798,7 +798,7 @@ PGPing PQping(const char *conninfo);
     connection parameters.  There are two accepted formats for these strings:
     plain keyword/value strings
     and URIs.  URIs generally follow
-    <ulink url="https://tools.ietf.org/html/rfc3986">RFC
+    <ulink url="https://datatracker.ietf.org/doc/html/rfc3986">RFC
     3986</ulink>, except that multi-host connection strings are allowed
     as further described below.
    </para>

doc/src/sgml/ref/psql-ref.sgml

@@ -2710,7 +2710,7 @@ lo_import 152801
           </indexterm>
           writes column values separated by commas, applying the quoting
           rules described in
-          <ulink url="https://tools.ietf.org/html/rfc4180">RFC 4180</ulink>.
+          <ulink url="https://datatracker.ietf.org/doc/html/rfc4180">RFC 4180</ulink>.
           This output is compatible with the CSV format of the server's
           <command>COPY</command> command.
           A header line with column names is generated unless