MM-24692: Add a since parameter to getGroups api (#14444)

* add a since parameter to getGroups api

* update for lint error

* when using since, return deleted groups as well.

* update flaky test, groups have same create time

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

model/client4.go

@@ -3781,6 +3781,9 @@ func (c *Client4) GetGroups(opts GroupSearchOpts) ([]*Group, *Response) {
 		opts.FilterAllowReference,
 		opts.Q,
 	)
+	if opts.Since > 0 {
+		path = fmt.Sprintf("%s&since=%v", path, opts.Since)
+	}
 	if opts.PageOpts != nil {
 		path = fmt.Sprintf("%s&page=%v&per_page=%v", path, opts.PageOpts.Page, opts.PageOpts.PerPage)
 	}