gh-125436: Doc: Add missing ``allow_unnamed_section`` parameter to ``ConfigParser`` documentation (#125437)

Add missing ``allow_unnamed_section`` parameter to ``ConfigParser`` doc, as well as to it's parent ``RawConfigParser``.
Split too long line on ``ConfigParser`` signature.
Add some sections about when some of ``RawConfigParser`` parameters were added.

Doc/library/configparser.rst

@@ -942,7 +942,13 @@ interpolation if an option used is not defined elsewhere. ::
 ConfigParser Objects
 --------------------
 
-.. class:: ConfigParser(defaults=None, dict_type=dict, allow_no_value=False, delimiters=('=', ':'), comment_prefixes=('#', ';'), inline_comment_prefixes=None, strict=True, empty_lines_in_values=True, default_section=configparser.DEFAULTSECT, interpolation=BasicInterpolation(), converters={})
+.. class:: ConfigParser(defaults=None, dict_type=dict, allow_no_value=False, *, \
+                        delimiters=('=', ':'), comment_prefixes=('#', ';'), \
+                        inline_comment_prefixes=None, strict=True, \
+                        empty_lines_in_values=True, \
+                        default_section=configparser.DEFAULTSECT, \
+                        interpolation=BasicInterpolation(), converters={}, \
+                        allow_unnamed_section=False)
 
    The main configuration parser.  When *defaults* is given, it is initialized
    into the dictionary of intrinsic defaults.  When *dict_type* is given, it
@@ -990,6 +996,10 @@ ConfigParser Objects
    converter gets its own corresponding :meth:`!get*` method on the parser
    object and section proxies.
 
+   When *allow_unnamed_section* is ``True`` (default: ``False``),
+   the first section name can be omitted. See the
+   `"Unnamed Sections" section <#unnamed-sections>`_.
+
    It is possible to read several configurations into a single
    :class:`ConfigParser`, where the most recently added configuration has the
    highest priority. Any conflicting keys are taken from the more recent
@@ -1039,6 +1049,9 @@ ConfigParser Objects
       Raise a :exc:`MultilineContinuationError` when *allow_no_value* is
       ``True``, and a key without a value is continued with an indented line.
 
+   .. versionchanged:: 3.13
+      The *allow_unnamed_section* argument was added.
+
    .. method:: defaults()
 
       Return a dictionary containing the instance-wide defaults.
@@ -1295,18 +1308,30 @@ RawConfigParser Objects
                            comment_prefixes=('#', ';'), \
                            inline_comment_prefixes=None, strict=True, \
                            empty_lines_in_values=True, \
-                           default_section=configparser.DEFAULTSECT[, \
+                           default_section=configparser.DEFAULTSECT, \
-                           interpolation])
+                           interpolation=BasicInterpolation(), converters={}, \
+                           allow_unnamed_section=False)
 
    Legacy variant of the :class:`ConfigParser`.  It has interpolation
    disabled by default and allows for non-string section names, option
    names, and values via its unsafe ``add_section`` and ``set`` methods,
    as well as the legacy ``defaults=`` keyword argument handling.
 
+   .. versionchanged:: 3.2
+      *allow_no_value*, *delimiters*, *comment_prefixes*, *strict*,
+      *empty_lines_in_values*, *default_section* and *interpolation* were
+      added.
+
+   .. versionchanged:: 3.5
+      The *converters* argument was added.
+
    .. versionchanged:: 3.8
       The default *dict_type* is :class:`dict`, since it now preserves
       insertion order.
 
+   .. versionchanged:: 3.13
+      The *allow_unnamed_section* argument was added.
+
    .. note::
       Consider using :class:`ConfigParser` instead which checks types of
       the values to be stored internally.  If you don't want interpolation, you