expose new_timestamp function

[milyin]

Describe the release item

Expose this function into zenoh-c

    /// Generates a reception [`Timestamp`] with id=0x01.  
    /// This operation should be called if a timestamp is required for an incoming [`zenoh::Sample`](crate::Sample)
    /// that doesn't contain any timestamp.
    // tags{rust.new_reception_timestamp, api.timestamp.create.now}
    pub fn new_reception_timestamp() -> Timestamp {
        use std::time::{SystemTime, UNIX_EPOCH};

        let now = SystemTime::now().duration_since(UNIX_EPOCH).unwrap();
        Timestamp::new(now.into(), TimestampId::try_from([1]).unwrap())
    }

[milyin]

Now it's new_timestamp() : eclipse-zenoh/zenoh#1091

[milyin]

Depends on eclipse-zenoh/zenoh#1179

[DenisBiryukov91]

Resolved by #519.