feat(settings): add setting to set number of suggested dates

paperless.conf.example

@@ -69,6 +69,7 @@
 #PAPERLESS_POST_CONSUME_SCRIPT=/path/to/an/arbitrary/script.sh
 #PAPERLESS_FILENAME_DATE_ORDER=YMD
 #PAPERLESS_FILENAME_PARSE_TRANSFORMS=[]
+#PAPERLESS_NUMBER_OF_SUGGESTION_DATES=5
 #PAPERLESS_THUMBNAIL_FONT_NAME=
 #PAPERLESS_IGNORE_DATES=
 #PAPERLESS_ENABLE_UPDATE_CHECK=