[feat] engines: add dogpile (general, news, images, videos)

Add support for the Dogpile search engine, found at:

https://seirdy.one/posts/2021/03/10/search-engines-with-own-indexes/

It seems to use the same index as startpage because results are similar and they
share the ``qadf`` (Safe-Search) request parameter.

searx/utils.py

@@ -813,7 +813,7 @@ def parse_duration_string(duration_str: str) -> timedelta | None:
 
 
 # Format the video duration
-def format_duration(duration):
+def format_duration(duration: str | int) -> str:
     seconds = int(duration)
     length = time.gmtime(seconds)
     if length.tm_hour: