[pholder] add support (#2568 #9067)

* feat: extractor for pholder.com
    Closes #2568
* feat[pholder]: support gallery_id properly and tags
* doc[text.nameext_from_name]: minor typo in docstring

* remove '__init__' & 'request' methods and 'json' import
* use 'text.nameext_from_url' to ensure a 'filename' value
* fix 'imgur' links by disabling auto-Referer
* fix 'data["id"].partition()' call
    'partition' returns 3 elements
* use 'item["_source"]' data directly
* remove unused supportedsites overwrite
* catch all exceptions in '_thumb_resolution'
    fixes "KeyError: 'width'"
* use 'author' name for user folders

---------

Co-authored-by: Mike Fährmann <mike_faehrmann@web.de>

docs/configuration.rst

@@ -1006,6 +1006,7 @@ Default
         ``4chanarchives`` |
         ``archivedmoe``   |
         ``nsfwalbum``     |
+        ``pholder``       |
         ``tumblrgallery``
     ``true``
         otherwise

docs/supportedsites.md

@@ -799,6 +799,12 @@ Consider all listed sites to potentially be NSFW.
     <td>Collections, individual Images, Search Results, User Profiles</td>
     <td></td>
 </tr>
+<tr id="pholder" title="pholder">
+    <td>pholder</td>
+    <td>https://pholder.com/</td>
+    <td>Search Results, Subreddits, User Profiles</td>
+    <td></td>
+</tr>
 <tr id="photovogue" title="photovogue">
     <td>PhotoVogue</td>
     <td>https://www.vogue.com/photovogue/</td>