Default to keeping field key when getting record key

smart-modules/assign-record-key/SmartModule.toml

···
 [[params]]
 name = "key"
 description = "The json field that should become the record key"
+
+[[params]]
+name = "delete"
+description = "Wether to delete the field when promoting it to record key"

smart-modules/assign-record-key/src/lib.rs

···
 use fluvio_smartmodule::{RecordData, Result, SmartModuleRecord, smartmodule};
 use serde_json::Value;
 
-static CRITERIA: OnceLock<String> = OnceLock::new();
+static KEY: OnceLock<String> = OnceLock::new();
+static DELETE: OnceLock<bool> = OnceLock::new();
 
 #[smartmodule(map)]
 pub fn map(record: &SmartModuleRecord) -> Result<(Option<RecordData>, RecordData)> {
···
     let obj = value
         .as_object_mut()
         .ok_or(eyre!("Failed to parse value"))?;
-    let key = obj
-        .remove(CRITERIA.get().ok_or(eyre!("Invalid state"))?)
-        .ok_or(eyre!("Key missing in record"))?;
+
+    let field_key = KEY.get().expect("Invalid state");
+    let record_key = if DELETE.get().is_some() {
+        obj.remove(field_key)
+            .ok_or(eyre!(format!("Key missing in record")))?
+            .to_string()
+    } else {
+        obj.get(field_key)
+            .ok_or(eyre!("Field missing in record"))?
+            .to_string()
+    };
 
-    Ok((
-        Some(key.to_string().into()),
-        value.to_string().as_str().into(),
-    ))
+    Ok((Some(record_key.into()), value.to_string().as_str().into()))
 }
 
 #[smartmodule(init)]
 fn init(params: SmartModuleExtraParams) -> Result<()> {
+    if params.get("delete").is_some() {
+        DELETE
+            .set(true)
+            .map_err(|_| eyre!("Failed to set input param"))?;
+    }
+
     if let Some(key) = params.get("key") {
-        CRITERIA
-            .set(key.clone())
+        KEY.set(key.clone())
             .map_err(|err| eyre!("failed setting key: {:#?}", err))
     } else {
         Err(SmartModuleInitError::MissingParam("key".to_string()).into())