[MM-17069] Api endpoint to unread a channel (#11794)

* [MM-17069] endpoint to unread a channel from post

* [MM-17069] update mock

* [MM-17069] first passing test

* [MM-17069] fix SQL typo

* [MM-17069] fix msgCount

* add tests

* [MM-17069] Fix tests

* [MM-16069] Remove trash, add comments

* [MM-16069] Add message to errors

* [MM-17069] fix go fmt

* [MM-17069] return an UnreadChannel response

* [MM-17069] added unauthorized test

* [MM-17069] fix operator

* [MM-17069] refactor tests

* [MM-16069] back to green tests

* [MM-17069] change url to include user

* [MM-17069] Fixing code review comments

* [MM-17069] One shouldn't fix manually what a machine can fix better

* [MM-17069] change response type, update tests

* [MM-17069] fix permission error

* [MM-17069] Add tests for edit_other_users permission

* [MM-17069] no magic numbers

model/client4.go

@@ -2480,6 +2480,16 @@ func (c *Client4) PatchPost(postId string, patch *PostPatch) (*Post, *Response)
 	return PostFromJson(r.Body), BuildResponse(r)
 }
 
+// SetPostUnread marks channel where post belongs as unread on the time of the provided post.
+func (c *Client4) SetPostUnread(userId string, postId string) *Response {
+	r, err := c.DoApiPost(c.GetUserRoute(userId)+c.GetPostRoute(postId)+"/set_unread", "")
+	if err != nil {
+		return BuildErrorResponse(r, err)
+	}
+	defer closeBody(r)
+	return BuildResponse(r)
+}
+
 // PinPost pin a post based on provided post id string.
 func (c *Client4) PinPost(postId string) (bool, *Response) {
 	r, err := c.DoApiPost(c.GetPostRoute(postId)+"/pin", "")