Add radarr config option for setting minimum availability

[AhmedNSidd]

Description

I was noticing that some movies that my family added to the Plex Watchlist weren't being downloaded automatically. Upon further investigation, this was because they had not been fully released, and instead were just released in cinemas. Currently Overseerr offers a configuration option for setting a minimum availability for media requests in Radarr, so I thought it'd be appropriate to have an option for this in Watchlistarr as well.

Checklist

• [X] Documentation Updated
• [X] sbt scalafmtAll Run (and optionally sbt scalafmtSbt)
• [ ] At least one approval from a codeowner