Added is:first-msg search option (#3700)

* added first-msg for flag predicate

* Update CHANGELOG.md

* Update changelog entry phrasing

Co-authored-by: pajlada <rasmus.karlsson@pajlada.com>

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unversioned
 
+- Minor: Added `is:first-msg` search option. (#3700)
 - Minor: Added quotation marks in the permitted/blocked Automod messages for clarity. (#3654)
 - Minor: Adjust large stream thumbnail to 16:9 (#3655)
 - Minor: Fixed being unable to load Twitch Usercards from the `/mentions` tab. (#3623)

src/messages/search/MessageFlagsPredicate.cpp

@@ -28,6 +28,10 @@ MessageFlagsPredicate::MessageFlagsPredicate(const QString &flags)
         {
             this->flags_.set(MessageFlag::System);
         }
+        else if (flag == "first-msg")
+        {
+            this->flags_.set(MessageFlag::FirstMessage);
+        }
     }
 }