[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/post.go

@@ -274,6 +274,14 @@ type GetPostsOptions struct {
 	Direction                string // Only accepts up|down. Indicates the order in which to send the items.
 }
 
+type PostCountOptions struct {
+	// Only include posts on a specific team. "" for any team.
+	TeamId          string
+	MustHaveFile    bool
+	MustHaveHashtag bool
+	ExcludeDeleted  bool
+}
+
 func (o *Post) Etag() string {
 	return Etag(o.Id, o.UpdateAt)
 }