[MM-43917] Cloud Freemium limits API: messages/posts (#20152)

* WIP - Add api and app funcs

* Add test cases

* Add utils testcases

* Exclude deleted posts

* Add doc for func

* Move api from cloud to usage

* Allow api access to authenticated users

* Change int to int64

* Fix lint issue

* Simplify err check

Co-authored-by: Ashish Bhate <ashish.bhate@mattermost.com>

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Ashish Bhate <ashish.bhate@mattermost.com>

model/client4.go

@@ -324,6 +324,10 @@ func (c *Client4) cloudRoute() string {
 	return "/cloud"
 }
 
+func (c *Client4) usageRoute() string {
+	return "/usage"
+}
+
 func (c *Client4) testEmailRoute() string {
 	return "/email/test"
 }
@@ -8078,3 +8082,18 @@ func (c *Client4) GetAppliedSchemaMigrations() ([]AppliedMigration, *Response, e
 	}
 	return list, BuildResponse(r), nil
 }
+
+// Usage Section
+
+// GetPostsUsage returns rounded off total usage of posts for the instance
+func (c *Client4) GetPostsUsage() (*PostsUsage, *Response, error) {
+	r, err := c.DoAPIGet(c.usageRoute()+"/posts", "")
+	if err != nil {
+		return nil, BuildResponse(r), err
+	}
+	defer closeBody(r)
+
+	var usage *PostsUsage
+	err = json.NewDecoder(r.Body).Decode(&usage)
+	return usage, BuildResponse(r), err
+}