MM-23935 extend session expiry on user activity (#14275)

* MM-23935  extend session expiry on user activity

- if user types anything before a session expires the session will be extended to now + session length

- ensures new session expiries are not written to DB too frequently

- new session store func for updating session ExpiresAt

- session length defaults for mobile and web/ldap changed from 180 days to 30 days

tests/test-config.json

@@ -33,6 +33,7 @@
         "EnableUserAccessTokens": false,
         "AllowCorsFrom": "",
         "AllowCookiesForSubdomains": false,
+        "ExtendSessionLengthWithActivity": true,
         "SessionLengthWebInDays": 30,
         "SessionLengthMobileInDays": 30,
         "SessionLengthSSOInDays": 30,