Password Complexity Checks (#6230)

Add password complexity checks. The default settings require a lowercase, uppercase, number and a special character within passwords.

Co-Authored-By: T-M-A <maxim.tkachenko@gmail.com>
Co-Authored-By: Lanre Adelowo <adelowomailbox@gmail.com>
Co-Authored-By: guillep2k <18600385+guillep2k@users.noreply.github.com>
Co-Authored-By: Lauris BH <lauris@nix.lv>

docs/content/doc/advanced/config-cheat-sheet.en-us.md

@@ -208,6 +208,11 @@ Values containing `#` or `;` must be quoted using `` ` `` or `"""`.
 - `INTERNAL_TOKEN_URI`: **<empty>**: Instead of defining internal token in the configuration, this configuration option can be used to give Gitea a path to a file that contains the internal token (example value: `file:/etc/gitea/internal_token`)
 - `PASSWORD_HASH_ALGO`: **pbkdf2**: The hash algorithm to use \[pbkdf2, argon2, scrypt, bcrypt\].
 - `CSRF_COOKIE_HTTP_ONLY`: **true**: Set false to allow JavaScript to read CSRF cookie.
+- `PASSWORD_COMPLEXITY`: **lower,upper,digit,spec**: Comma separated list of character classes required to pass minimum complexity. If left empty or no valid values are specified, the default values will be used. Possible values are: 
+    - lower - use one or more lower latin characters
+    - upper - use one or more upper latin characters
+    - digit - use one or more digits
+    - spec - use one or more special characters as ``][!"#$%&'()*+,./:;<=>?@\^_{|}~`-`` and space symbol. 
 
 ## OpenID (`openid`)