Release v0.51.0

Added

• The ability to specify the DNS timeout via CLI arguments and configuration file (#333).
• The ability to set domain-specific fallback servers, like in general and private upstream configurations.

Changed

• The Fallbacks field of the proxy.Config is now an proxy.UpstreamConfig.
• Validation policy now restricts usage of empty non-nil upstream configurations for the PrivateRDNSUpstreamConfig, and Fallbacks fields of proxy.Config and will cause an error on call to Start.

Fixed

• Logging level for some QUIC-related errors (AdguardTeam/AdGuardHome#5285).