Proxy support

[DataFran]

Per your request on Discord:
Can you please add proxy support as an alternative solution to CloudFlare/Flaresolverr?

Prowlarr does this, and it has solved several CloudFlare blocked trackers for me, utilizing a Gluetun container's proxy service, rather than putting the entire container behind Gluetun.

[Casvt]

Note to self/contributor:

Offer settings for proxy type (HTTP(S), SOCKS4/5), hostname, port, credentials (username, password), and bypass rules. Then build URL and set it in environment variables. Use Bazarr implementation as reference. Exclusively uppercase variables is already sufficient. (Sub)Processes will take them over without extra configuration. Request sessions might cache values, and subprocess with session might be running (e.g. editing settings while searching for downloads), so to ensure all sessions use new value, we have to force a restart just like with hosting settings.