Use atomics instead of mutexes

Use atomics instead of mutexes to improve access on metrics. Therefor
also remove unneeded borrows.

src/webhooks.rs

@@ -74,7 +74,7 @@ impl JsonFilter {
         let regex = Regex::new(&self.regex).map_err(WebhookeyError::Regex)?;
 
         if let Some(value) = data.pointer(&self.pointer) {
-            if regex.is_match(&self.get_string(&value)?) {
+            if regex.is_match(&self.get_string(value)?) {
                 debug!("Regex `{}` for `{}` matches", &self.regex, &self.pointer);
 
                 return Ok(true);