Simplify self-signed certificates usage with HTTPS

Initially reported in https://github.com/ClickHouse/clickhouse-rs/issues/164

We have a few options:

- Add an example based on https://github.com/ClickHouse/clickhouse-rs/issues/134#issuecomment-2604317017
- Add an example on adding the cert into the OS trust store, see the first part of https://github.com/ClickHouse/clickhouse-rs/issues/164#issuecomment-2380918839
- Add a feature in the client, see the second part of https://github.com/ClickHouse/clickhouse-rs/issues/164#issuecomment-2380918839 + https://github.com/ClickHouse/clickhouse-rs/issues/164#issuecomment-2381262329

Start by reading the linked issue 164 and its referenced comments, including issue 134's comment, to compare the proposed approaches. The scope is not settled: done could mean a self-signed certificate example, OS trust-store guidance, or a client feature, so the chosen approach and its acceptance criteria need to be decided first.

Written by the indexing model from the issue text.