[MM-58492][MM-58523] Fixed some access control bugs around archived channels by replacing the permission check with HasPermissionToReadChannel (#27409)

* [MM-58492][MM-58523] Fixed some access control bugs around archived channels by replacing the permission check with HasPermissionToReadChannel

* Fix lint, add ChannelId to uploads

* Fix MMCTL tests and remove unnecessary check for the error message that doesn't work anyways

* Include channel map for getting flagged posts

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/api4/channel.go

@@ -758,7 +758,12 @@ func getPinnedPosts(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if !c.App.SessionHasPermissionToChannel(c.AppContext, *c.AppContext.Session(), c.Params.ChannelId, model.PermissionReadChannelContent) {
+	channel, err := c.App.GetChannel(c.AppContext, c.Params.ChannelId)
+	if err != nil {
+		c.Err = err
+		return
+	}
+	if !c.App.SessionHasPermissionToReadChannel(c.AppContext, *c.AppContext.Session(), channel) {
 		c.SetPermissionError(model.PermissionReadChannelContent)
 		return
 	}