[common] use 'parent' value as 'parent-metadata' default (#8525 #8604)

enable 'parent-metadata' by default for
'chevereto' & 'imagehost' (album/gallery) extractors

gallery_dl/extractor/chevereto.py

@@ -17,6 +17,7 @@ class CheveretoExtractor(BaseExtractor):
     basecategory = "chevereto"
     directory_fmt = ("{category}", "{user}", "{album}")
     archive_fmt = "{id}"
+    parent = True
 
     def _init(self):
         self.path = self.groups[-1]

gallery_dl/extractor/common.py

@@ -33,6 +33,7 @@ class Extractor():
     basecategory = ""
     basesubcategory = ""
     categorytransfer = False
+    parent = False
     directory_fmt = ("{category}",)
     filename_fmt = "{filename}.{extension}"
     archive_fmt = ""

gallery_dl/extractor/imagehosts.py

@@ -19,6 +19,7 @@ class ImagehostImageExtractor(Extractor):
     basecategory = "imagehost"
     subcategory = "image"
     archive_fmt = "{token}"
+    parent = True
     _https = True
     _params = None
     _cookies = None