Describe the bug
"Filter actions" are not saved using the export option to migrate a configuration

To Reproduce
Steps to reproduce the behavior:

1. Go to subscription management and add something to "Filter actions" on one feed subscription, then save
   
2. Go to "Import / Export" and export all your conf (here are extract with only the parts about that feed)
   feed_2021-12-22_8_114.json.txt
   feeds_2021-12-22.opml.xml.txt
3. Restore that conf on another FreshRSS install with the "Import" option
4. See that the "Filter actions" stays empty (the info doesn't even seem to be in the exported opml.xml file)

Expected behavior
Exporting all the configuration of the feed subscriptions (so also all fields modified, not only "Filter actions" if there are others)

Environment information (please complete the following information):
Export done on FreshRSS 1.19.0-dev (git) in a LXC container running debian OS with postgreSQL DB, import in FreshRSS official Docker alpine tag sqlite DB