Add Not filter to FilterType

To invert the result of filters.

src/webhooks.rs

@@ -93,6 +93,7 @@ impl JsonFilter {
 #[derive(Debug, Deserialize, Serialize)]
 #[serde(deny_unknown_fields, rename_all = "lowercase")]
 pub enum FilterType {
+    Not(Box<FilterType>),
     And(Vec<FilterType>),
     Or(Vec<FilterType>),
     #[serde(rename = "json")]
@@ -102,6 +103,7 @@ pub enum FilterType {
 impl FilterType {
     pub fn evaluate(&self, data: &serde_json::Value) -> Result<bool, WebhookeyError> {
         match self {
+            FilterType::Not(filter) => Ok(!filter.evaluate(data)?),
             FilterType::And(filters) => {
                 let (mut results, mut errors) = (Vec::new(), Vec::new());