eventmanager: add password notification check action

this action allow to send an email notification to users whose
password is about to expire

Signed-off-by: Nicola Murino <nicola.murino@gmail.com>

templates/email/password-expiration.html

@@ -0,0 +1,19 @@
+<!--
+Copyright (C) 2019-2022  Nicola Murino
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU Affero General Public License as published
+by the Free Software Foundation, version 3.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU Affero General Public License for more details.
+
+You should have received a copy of the GNU Affero General Public License
+along with this program.  If not, see <https://www.gnu.org/licenses/>.
+-->
+Hi {{.Username}},
+<br>
+<p>Your SFTPGo password {{if le .Days 0}}has expired{{else}}expires in {{.Days}} {{if eq .Days 1}}day{{else}}days{{end}}{{end}}.</p>
+<p>Please login to the WebClient and set a new password.</p>