[MM-23264] Get channel member counts by group (#14068)

* MM-23264 Add api endpoint for get groups with members in channel

Add store tests

Add tests for api func

Gofmt

Apply changes from code review

* MM-23264 Make store layers

* MM-23264 Check read permission on channel member counts

* Trigger CI

model/channel.go

@@ -128,6 +128,12 @@ type ChannelSearchOpts struct {
 	PerPage                *int
 }
 
+type ChannelMemberCountByGroup struct {
+	GroupId                     string `db:"-" json:"group_id"`
+	ChannelMemberCount          int64  `db:"-" json:"channel_member_count"`
+	ChannelMemberTimezonesCount int64  `db:"-" json:"channel_member_timezones_count"`
+}
+
 func (o *Channel) DeepCopy() *Channel {
 	copy := *o
 	if copy.SchemeId != nil {
@@ -181,6 +187,12 @@ func ChannelModerationsPatchFromJson(data io.Reader) []*ChannelModerationPatch {
 	return o
 }
 
+func ChannelMemberCountsByGroupFromJson(data io.Reader) []*ChannelMemberCountByGroup {
+	var o []*ChannelMemberCountByGroup
+	json.NewDecoder(data).Decode(&o)
+	return o
+}
+
 func (o *Channel) Etag() string {
 	return Etag(o.Id, o.UpdateAt)
 }