[girlswithmuscle] add support (#4493 #6016)

* [girlswithmuscle] init
* [girlswithmuscle]: fix metadata extraction (site layout change)
* [girlswithmuscle]: fix tags extraction (site layout change)
* update login code
* update 'post' extractor
* update 'gallery' extractor, rename to 'search' extractor
* update docs
* add test cases

---------

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

docs/configuration.rst

@@ -461,6 +461,7 @@ Description
     * ``e6ai`` (*)
     * ``e926`` (*)
     * ``exhentai``
+    * ``girlswithmuscle``
     * ``horne`` (R)
     * ``idolcomplex``
     * ``imgbb``

docs/gallery-dl.conf

@@ -328,6 +328,11 @@
         {
             "enabled": false
         },
+        "girlswithmuscle":
+        {
+            "username": "",
+            "password": ""
+        },
         "gofile":
         {
             "api-token": null,

docs/supportedsites.md

@@ -319,6 +319,12 @@ Consider all listed sites to potentially be NSFW.
     <td>Favorites, Pools, Posts, Redirects, Tag Searches</td>
     <td></td>
 </tr>
+<tr>
+    <td>Girls with Muscle</td>
+    <td>https://www.girlswithmuscle.com/</td>
+    <td>Posts, Search Results</td>
+    <td>Supported</td>
+</tr>
 <tr>
     <td>Gofile</td>
     <td>https://gofile.io/</td>