New: Add headers setting in webhook connection

(cherry picked from commit 78fb20282de73c0ea47375895a807235385d90e3)

frontend/src/Components/Form/KeyValueListInputItem.css

@@ -5,13 +5,19 @@
 
   &:last-child {
     margin-bottom: 0;
+    border-bottom: 0;
   }
 }
 
-.inputWrapper {
+.keyInputWrapper {
   flex: 1 0 0;
 }
 
+.valueInputWrapper {
+  flex: 1 0 0;
+  min-width: 40px;
+}
+
 .buttonWrapper {
   flex: 0 0 22px;
 }
@@ -20,4 +26,10 @@
 .valueInput {
   width: 100%;
   border: none;
+  background-color: transparent;
+  color: var(--textColor);
+
+  &::placeholder {
+    color: var(--helpTextColor);
+  }
 }