[PLT-7362] Option to add user to channel if mentioned user is not currently in the channel (#7619)

* Option to add user to channel if mentioned user is not currently in the channel

* instead of link from server, just add component on client side to add channel member

* change implementation using post.props

* do clean up and add test

* sanitize post.props['add_channel_member'] on post creation

* move sanitize to app.CreatePost and also apply to app.UpdatePost

model/post_test.go

@@ -123,3 +123,46 @@ func TestPostIsSystemMessage(t *testing.T) {
 		t.Fatalf("TestPostIsSystemMessage failed, expected post2.IsSystemMessage() to be true")
 	}
 }
+
+func TestPostSanitizeProps(t *testing.T) {
+	post1 := &Post{
+		Message: "test",
+	}
+
+	post1.SanitizeProps()
+
+	if post1.Props[PROPS_ADD_CHANNEL_MEMBER] != nil {
+		t.Fatal("should be nil")
+	}
+
+	post2 := &Post{
+		Message: "test",
+		Props: StringInterface{
+			PROPS_ADD_CHANNEL_MEMBER: "test",
+		},
+	}
+
+	post2.SanitizeProps()
+
+	if post2.Props[PROPS_ADD_CHANNEL_MEMBER] != nil {
+		t.Fatal("should be nil")
+	}
+
+	post3 := &Post{
+		Message: "test",
+		Props: StringInterface{
+			PROPS_ADD_CHANNEL_MEMBER: "no good",
+			"attachments":            "good",
+		},
+	}
+
+	post3.SanitizeProps()
+
+	if post3.Props[PROPS_ADD_CHANNEL_MEMBER] != nil {
+		t.Fatal("should be nil")
+	}
+
+	if post3.Props["attachments"] == nil {
+		t.Fatal("should not be nil")
+	}
+}