Fix password charset to be URI-safe

PR #121 strengthened the password but used string.punctuation which
includes > + [ ] @ : / and other chars that are invalid or require
percent-encoding in a MySQL URI (used in mysql-mgmt --bootstrap and
SQLAlchemy connection strings). Restrict to alphanumeric only: 24
chars of [A-Za-z0-9] gives ~143 bits of entropy which is sufficient.

Author: szachovy

src/crypto.py

@@ -65,7 +65,7 @@ def generate_mysql_root_password() -> str:
 
     @staticmethod
     def generate_mysql_superset_password() -> str:
-        charset = string.ascii_letters + string.digits + "!@#$%&*-_=+[]<>?"
+        charset = string.ascii_letters + string.digits
         return "".join(secrets.choice(charset) for _ in range(24))
 
     @staticmethod