mrhlpr: msg_filter_add_label: add trailer line

Add basic logic to detect when we should insert a trailer line at the
end of the commit message, before adding the CI label.

mrhlpr/data/msg_filter_add_label.py

@@ -17,6 +17,7 @@ if not label_line:
 label = f"{label_line.split(']', 1)[0]}]"
 label_found = False
 line_number = 0
+empty_lines = 0
 for line in sys.stdin:
     line = line.rstrip()
     line_number += 1
@@ -24,6 +25,9 @@ for line in sys.stdin:
     if label in line:
         label_found = True
 
+    if line == "":
+        empty_lines += 1
+
     print(line)
 
 if label_found:
@@ -32,4 +36,8 @@ if label_found:
 if line_number == 2:
     print()
 
+# Add empty line before starting trailer section of commit message
+if line_number >= 3 and empty_lines < 2:
+    print()
+
 print(label_line)