Disable setting fields in case we use environment variables

src/Core/Config/Capability/IManageConfigValues.php

@@ -58,6 +58,16 @@ interface IManageConfigValues
 	 */
 	public function get(string $cat, string $key = null, $default_value = null);
 
+	/**
+	 * Returns true, if the current config cannot be changed
+	 *
+	 * @param string $cat The category of the configuration value
+	 * @param string $key The configuration key to query
+	 *
+	 * @return bool true, if set is disabled
+	 */
+	public function isSetDisabled(string $cat, string $key): bool;
+
 	/**
 	 * Sets a configuration value for system config
 	 *