[pixiv] implement workaround for 'limit_sanity_level' works

(#4327, #4747, #5054, #5435, #5651, #5655)

Metadata should be ~95% identical (there might be some 'date' differences)
and there could be issues with R-18 works, as these require some URL
manipulation to transform /c/250x250_80_a2/ thumbnail URLs into
/img-original/ ones.

docs/configuration.rst

@@ -3525,6 +3525,16 @@ Description
     A value of ``0`` means no limit.
 
 
+extractor.pixiv.sanity
+----------------------
+Type
+    ``bool``
+Default
+    ``true``
+Description
+    Try to fetch ``limit_sanity_level`` works via web API.
+
+
 extractor.plurk.comments
 ------------------------
 Type