[MM-44765] Add API method for getting post's information from permalink (#21518)

* add api for getting post's information

* add information about current user state

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>

model/client4.go

@@ -8540,6 +8540,20 @@ func (c *Client4) GetNewTeamMembersSince(teamID string, timeRange string, page i
 	return newTeamMembersList, BuildResponse(r), nil
 }
 
+func (c *Client4) GetPostInfo(postId string) (*PostInfo, *Response, error) {
+	r, err := c.DoAPIGet(c.postRoute(postId)+"/info", "")
+	if err != nil {
+		return nil, BuildResponse(r), err
+	}
+	defer closeBody(r)
+
+	var info *PostInfo
+	if err = json.NewDecoder(r.Body).Decode(&info); err != nil {
+		return nil, nil, NewAppError("GetPostInfo", "api.unmarshal_error", nil, "", http.StatusInternalServerError).Wrap(err)
+	}
+	return info, BuildResponse(r), nil
+}
+
 func (c *Client4) AcknowledgePost(postId, userId string) (*PostAcknowledgement, *Response, error) {
 	r, err := c.DoAPIPost(c.userRoute(userId)+c.postRoute(postId)+"/ack", "")
 	if err != nil {

model/post_info.go

@@ -0,0 +1,15 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+type PostInfo struct {
+	ChannelId          string      `json:"channel_id"`
+	ChannelType        ChannelType `json:"channel_type"`
+	ChannelDisplayName string      `json:"channel_display_name"`
+	HasJoinedChannel   bool        `json:"has_joined_channel"`
+	TeamId             string      `json:"team_id"`
+	TeamType           string      `json:"team_type"`
+	TeamDisplayName    string      `json:"team_display_name"`
+	HasJoinedTeam      bool        `json:"has_joined_team"`
+}