fix: [feed-generator] Revert back the event initial search to use the index endpoint instead of RestSearch

Relying on RestSearch was offering more flexibility than index in terms of filtering options,
however, it might introduce a significant overhead potentially leading to timeout.

examples/feed-generator/generate.py

@@ -62,7 +62,7 @@ def saveManifest(manifest):
 if __name__ == '__main__':
     misp = init()
     try:
-        events = misp.search(metadata=True, limit=entries, **filters, pythonify=True)
+        events = misp.search_index(minimal=True, limit=entries, **filters, pythonify=False)
     except Exception as e:
         print(e)
         sys.exit("Invalid response received from MISP.")