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>

api4/group.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"net/http"
+	"strconv"
 	"strings"
 
 	"github.com/mattermost/mattermost-server/v5/audit"
@@ -730,6 +731,16 @@ func getGroups(c *Context, w http.ResponseWriter, r *http.Request) {
 		opts.NotAssociatedToChannel = channelID
 	}
 
+	sinceString := r.URL.Query().Get("since")
+	if len(sinceString) > 0 {
+		since, parseError := strconv.ParseInt(sinceString, 10, 64)
+		if parseError != nil {
+			c.SetInvalidParam("since")
+			return
+		}
+		opts.Since = since
+	}
+
 	groups, err := c.App.GetGroups(c.Params.Page, c.Params.PerPage, opts)
 	if err != nil {
 		c.Err = err