We have one site setting, `auto_silence_fast_typers_max_trust_level`, which expects a trust level. However, the type is set to integer, which makes it very hard for a layman to enter the correct thing.
This PR changes the type of the site setting to the `TrustLevelSetting` enum.
The use of these are interchangeable in the back-end, since `SiteSetting.auto_silence_fast_typers_max_trust_level` still returns the integer value with the enum.