PLT-7705: API to get data retention policy. (#7539)

* PLT-7705: API to get data retention policy.

* Fix review comments.

api4/data_retention.go

@@ -0,0 +1,30 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package api4
+
+import (
+	"net/http"
+
+	l4g "github.com/alecthomas/log4go"
+
+	"github.com/mattermost/mattermost-server/utils"
+)
+
+func (api *API) InitDataRetention() {
+	l4g.Debug(utils.T("api.data_retention.init.debug"))
+
+	api.BaseRoutes.DataRetention.Handle("/policy", api.ApiSessionRequired(getPolicy)).Methods("GET")
+}
+
+func getPolicy(c *Context, w http.ResponseWriter, r *http.Request) {
+
+	// No permission check required.
+
+	if policy, err := c.App.GetDataRetentionPolicy(); err != nil {
+		c.Err = err
+		return
+	} else {
+		w.Write([]byte(policy.ToJson()))
+	}
+}