fix: Set required config (to an empty value

Flask AppBuilder 5, for some reason, requires `RECAPTCHA_PUBLIC_KEY` to be set, or the UI cannot be used, and the following error is emitted on the container console:

```
  File "/stackable/app/lib64/python3.11/site-packages/superset/views/base.py", line 417, in cached_common_bootstrap_data
    frontend_config["RECAPTCHA_PUBLIC_KEY"] = app.config["RECAPTCHA_PUBLIC_KEY"]
                                              ~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^
KeyError: 'RECAPTCHA_PUBLIC_KEY'
```

Author: NickLarsenNZ

rust/operator-binary/src/config.rs

@@ -61,6 +61,13 @@ pub fn add_superset_config(
         SupersetConfigOptions::LoggingConfigurator.to_string(),
         "StackableLoggingConfigurator()".into(),
     );
+    // Flask AppBuilder requires this to be set, otherwise the web ui cannot be used.
+    // We chose to make it an expression in case the user wants to override it through
+    // configurationOverrides (though it would require other settings like the private key too).
+    config.insert(
+        SupersetConfigOptions::RecaptchaPublicKey.to_string(),
+        "''".to_owned(),
+    );
 
     append_authentication_config(config, authentication_config)?;
 

rust/operator-binary/src/crd/mod.rs

@@ -110,6 +110,9 @@ pub enum SupersetConfigOptions {
     AuthOpaRule,
     AuthOpaCacheMaxEntries,
     AuthOpaCacheTtlInSec,
+    // Flask AppBuilder (currently) requires this to be set, even if not used,
+    // otherwise the web UI cannot be used,
+    RecaptchaPublicKey,
 }
 
 #[versioned(
@@ -425,6 +428,11 @@ impl FlaskAppConfigOptions for SupersetConfigOptions {
             SupersetConfigOptions::AuthOpaRule => PythonType::StringLiteral,
             SupersetConfigOptions::AuthOpaCacheMaxEntries => PythonType::IntLiteral,
             SupersetConfigOptions::AuthOpaCacheTtlInSec => PythonType::IntLiteral,
+            // Flask AppBuilder (currently) requires this option to be set (even if empty).
+            // If we set it to a string, the user cannot then get it from an expression in
+            // configOverrides. So we make it an expression, but will need to manually quote the
+            // empty string as a default.
+            SupersetConfigOptions::RecaptchaPublicKey => PythonType::Expression,
         }
     }
 }