Remember login for a month by default (#30150)

Previously, the default was a week.
As most instances don't set the setting, this leads to a bad user
experience by default.

## ⚠️ Breaking

If your instance requires a high level of security,
you may want to set `[security].LOGIN_REMEMBER_DAYS` so that logins are
not valid as long.

---------

Co-authored-by: Jason Song <i@wolfogre.com>

docs/content/administration/config-cheat-sheet.en-us.md

@@ -528,7 +528,7 @@ And the following unique queues:
 - `INSTALL_LOCK`: **false**: Controls access to the installation page. When set to "true", the installation page is not accessible.
 - `SECRET_KEY`: **\<random at every install\>**: Global secret key. This key is VERY IMPORTANT, if you lost it, the data encrypted by it (like 2FA secret) can't be decrypted anymore.
 - `SECRET_KEY_URI`: **_empty_**: Instead of defining SECRET_KEY, this option can be used to use the key stored in a file (example value: `file:/etc/gitea/secret_key`). It shouldn't be lost like SECRET_KEY.
-- `LOGIN_REMEMBER_DAYS`: **7**: Cookie lifetime, in days.
+- `LOGIN_REMEMBER_DAYS`: **31**: How long to remember that a user is logged in before requiring relogin (in days).
 - `COOKIE_REMEMBER_NAME`: **gitea\_incredible**: Name of cookie used to store authentication
    information.
 - `REVERSE_PROXY_AUTHENTICATION_USER`: **X-WEBAUTH-USER**: Header name for reverse proxy