[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

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

scripts/supportedsites.py

@@ -55,6 +55,7 @@ CATEGORY_MAP = {
     "fashionnova"    : "Fashion Nova",
     "furaffinity"    : "Fur Affinity",
     "furry34"        : "Furry 34 com",
+    "girlswithmuscle": "Girls with Muscle",
     "hatenablog"     : "HatenaBlog",
     "hbrowse"        : "HBrowse",
     "hentai2read"    : "Hentai2Read",
@@ -458,6 +459,7 @@ AUTH_MAP = {
     "flickr"         : _OAUTH,
     "furaffinity"    : _COOKIES,
     "furbooru"       : "API Key",
+    "girlswithmuscle": "Supported",
     "horne"          : "Required",
     "idolcomplex"    : "Supported",
     "imgbb"          : "Supported",