Allow some settings for MySQL compatibility

[alexey-milovidov]

Changelog category (leave one):

• Improvement

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

The server will allow using the SQL_* settings such as SQL_AUTO_IS_NULL as no-ops for MySQL compatibility. This closes #49927.

[alexey-milovidov]

For clang-17.

[robot-clickhouse-ci-2]

This is an automated comment for commit 4dbe5b8 with description of existing statuses. It's updated for the latest CI running
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[alexey-milovidov]

Sadly, we use our own mini-language (comma-separated values) inside XML.
The right way would be:

<custom_settings_prefixes>
    <prefix>SQL_</prefix>
    <prefix>custom_</prefix>
</custom_settings_prefixes>