cli: Method to drop the last progress bar message

Useful to create "temporary" messages, will be used to reduce the
"Running scriptlet" / "Stop scriptlet" rpm transaction noise.

include/libdnf5-cli/progressbar/progress_bar.hpp

@@ -95,6 +95,8 @@ public:
 
     // messages
     void add_message(MessageType type, const std::string & message) { messages.emplace_back(type, message); }
+    /// remove the last message
+    void pop_message();
     const std::vector<Message> & get_messages() const noexcept { return messages; }
 
     // auto-finish feature; turn off if you want to handle state manually

libdnf5-cli/progressbar/progress_bar.cpp

@@ -159,6 +159,13 @@ void ProgressBar::set_total_ticks(int64_t value) {
 }
 
 
+void ProgressBar::pop_message() {
+    if (!messages.empty()) {
+        messages.pop_back();
+    }
+}
+
+
 std::ostream & operator<<(std::ostream & os, ProgressBar & bar) {
     bar.to_stream(os);
     return os;