Support disabling of HTTPS RR

[mxinden]

Firefox supports disabling DNS HTTPS RR. Implement support in the happy eyeballs config.

happy-eyeballs/src/lib.rs

Lines 482 to 489 in a43abfd

	pub struct NetworkConfig {
	/// Supported HTTP versions
	pub http_versions: HttpVersions,
	/// IP connectivity and preference
	pub ip: IpPreference,
	/// Alternative services from previous connections
	pub alt_svc: Vec<AltSvc>,
	}

[mxinden]

@KershawChang would you mind linking the relevant Firefox prefs here? Is it only network.dns.use_https_rr_as_altsvc?