[IPTorrents] Add option to search freeleech only on IPTorrents

[GordonFreemanK]

Based on the TorrentLeech implementation (IPT uses query string params), tested locally with IPT

Tested the following with the option on:

• empty text search (from the web ui): returns only torrents tagged Freelech
• some text search with a movie name: same as above
• empty torznab search i.e. https://localhost:44307/api/v2.0/indexers/iptorrents/results/torznab/ (with Postman): returns only downloadVolumeFactor=0 results
• movie torznab search i.e. https://localhost:44307/api/v2.0/indexers/iptorrents/results/torznab/api?apikey={apiKey}&t=movie&extended=1&imdbid=1217209&password=1&cat=2000 : same as above

Same test cases with the option off, and as expected non-freeleech items are returned as well

[ngosang]

Thank you!

[ilike2burnthing]

v0.17.437