Add setLogger function to OpmLog

opm/common/OpmLog/OpmLog.cpp

@@ -53,6 +53,16 @@ namespace Opm {
         }
     }
 
+    bool OpmLog::setLogger(const std::shared_ptr<Logger>& logger) {
+        if (!m_logger) {
+            m_logger = logger;
+            return true;
+        } else if (m_logger.get() == logger.get()){
+            return true;
+        } else {
+            return false; // Logger was set to something else
+        }
+    }
 
     std::shared_ptr<Logger> OpmLog::getLogger() {
         if (!m_logger)

opm/common/OpmLog/OpmLog.hpp

@@ -90,6 +90,22 @@ class OpmLog {
 
     static bool stdoutIsTerminal();
 
+    /**
+     * @brief Sets the global logger instance for the `OpmLog` class.
+     *
+     * This static function allows setting a shared pointer to a `Logger` instance
+     * as the global logger. It ensures that the logger is set only if it has not
+     * been previously set or if the provided logger is the same as the existing one.
+     * This function prevents changing the logger once it has been set to a different instance.
+     * If the logger is already set to a different instance, the function will return `false`.
+     *
+     * @param logger A `std::shared_ptr` to a `Logger` instance that will be set as the global logger.
+     *
+     * @return `true` if the logger was successfully set or if the same logger was already set.
+     *         `false` if a different logger had already been set and the new logger could not be set.
+     */
+    static bool setLogger(const std::shared_ptr<Logger>& logger);
+
 private:
     static std::shared_ptr<Logger> getLogger();
     static std::shared_ptr<Logger> m_logger;