Implement turn server settings

this fills out the infos in /_matrix/client/r0/voip/turnServer with
values specified in the server config

src/database.rs

@@ -74,6 +74,14 @@ pub struct Config {
     trusted_servers: Vec<Box<ServerName>>,
     #[serde(default = "default_log")]
     pub log: String,
+    #[serde(default)]
+    turn_username: String,
+    #[serde(default)]
+    turn_password: String,
+    #[serde(default = "Vec::new")]
+    turn_uris: Vec<String>,
+    #[serde(default = "default_turn_ttl")]
+    turn_ttl: u64,
 
     #[serde(flatten)]
     catchall: BTreeMap<String, IgnoredAny>,
@@ -131,6 +139,10 @@ fn default_log() -> String {
     "info,state_res=warn,rocket=off,_=off,sled=off".to_owned()
 }
 
+fn default_turn_ttl() -> u64 {
+    60 * 60 * 24
+}
+
 #[cfg(feature = "sled")]
 pub type Engine = abstraction::sled::Engine;