feat: Add TMDB API key setting

[cocool97]

This MR aims to add a TMDB feature, that would be useful to download posters, metadatas & summaries for movies & shows.

This is currently a Draft, and here is a list of planned features :

• Add TMDB API Key setting
• Add a tmdb_id field on torrents
• Add a server side api forwarder for TMDB (https://github.com/cyruzin/golang-tmdb)
• Split torrent list API endpoint into two: main page listing (returning basic informations) and torrent listing (returning torrent specific informations). To reduce network fingerprint as server list in polled regularly. This feature could be developed and merged without this MR)
• Add a button when adding a new torrent to automatically get TMDB id if possible (based on torrent name), or manually set it if wanted. (Only if TMDB APi key has been provided)
• Display TMDB informations on torrent page for torrent (summary for example + episode summary for shows + rating) (not implementing it for Android application)

[trinity-aml]

I have done this or almost that in my fork https://github.com/trinity-aml/TorrServer. Work good, but not perfect ;)

[cocool97]

Oh nice ! Why don't you merge it upstream ?