[redbust] add support (#6759 #6918 #7043)

* init - Redbust.com Support
* Added Test
    Could use a second set of eyes on this
* update 'gallery' extractor
    - extract more metadata
    - simplify image extraction
    - support legacy galleries
* add tests
* update 'image' extractor
* add 'tag' extractor
* add 'archive' extractor
* restrict 'image' extractor pattern
* update docs/supportedsites
* replace quotes inside f-string

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

gallery_dl/extractor/__init__.py

@@ -145,6 +145,7 @@ modules = [
     "reactor",
     "readcomiconline",
     "realbooru",
+    "redbust",
     "reddit",
     "redgifs",
     "rule34us",