Add experimental availability to Timeseries

Author: barboraplasovska

DatadogRUM/Sources/RUMConfiguration.swift

@@ -334,6 +334,7 @@ extension RUM {
         /// timeseries events scoped to the RUM session. Requires `vitalsUpdateFrequency` to be set.
         ///
         /// Default: `false`.
+        @available(*, message: "This API is experimental and may change in future releases")
         public var enableTimeseries: Bool
 
         /// The default number of samples collected before a timeseries batch is flushed.