[Web][Restic][Dovecot][Dockerapi] Add restic backups with restore in the UI

- Scheduled, encrypted backups to S3, SFTP, REST or a local folder (new restic-mailcow container)
- Restore of mailboxes and whole domains in the UI, also deleted ones, for admins and domain admins
- Scope set by RESTIC_BACKUP_MODE in mailcow.conf (all, data, config)
- Optional backup before updates (update.sh), helper-scripts/restic.sh for a full restore

tests/python/backup/support.py

@@ -0,0 +1,51 @@
+# Shared helpers of the backup runner tests: fake database rows and a settable clock
+import datetime
+import os
+import time
+
+
+class Cursor:
+  def __init__(self, rows):
+    self.rows = rows
+    self.rowcount = len(rows)
+    self.lastrowid = 1
+
+  def fetchone(self):
+    return self.rows[0] if self.rows else None
+
+  def fetchall(self):
+    return self.rows
+
+  def __iter__(self):
+    return iter(self.rows)
+
+
+class FakeDatetime(datetime.datetime):
+  current = None
+
+  @classmethod
+  def now(cls, tz=None):
+    return cls.current
+
+
+class Clock:
+  # datetime module for a runner: datetime.now() returns the set time
+  timedelta = datetime.timedelta
+  date = datetime.date
+  datetime = FakeDatetime
+
+
+# Local time zone of the process for one test (cleaned up with the test case); the fake clock is reset as well
+def use_timezone(test, name):
+  old = os.environ.get('TZ')
+
+  def restore():
+    if old is None:
+      os.environ.pop('TZ', None)
+    else:
+      os.environ['TZ'] = old
+    time.tzset()
+    FakeDatetime.current = None
+  test.addCleanup(restore)
+  os.environ['TZ'] = name
+  time.tzset()