Respect remote_url_allow_hosts for MySQL and PostgreSQL table functions

Why it matters

This feature improves security by restricting which remote hosts can be accessed through the MySQL and PostgreSQL table functions, ensuring that only hosts allowed by the remote_url_allow_hosts configuration can be queried.

How to use it

Configure the remote_url_allow_hosts setting in your ClickHouse server configuration to specify permitted remote hosts. The MySQL and PostgreSQL table functions will then respect this whitelist automatically when connecting to external databases.