Add validation of IP addresses and domains in settings

[rschu1ze]

Many settings in ClickHouse's configuration file specify hosts in the form of IP addresses (12.13.14.15) or domains (mail.stanford.edu). Example:

<clickhouse>
    <zookeeper>
        <node ...>
            <host> 172.31.0.47</host>
            ...
        </node>
    </zookeeper>
</clickhouse>

Many similar settings exist. As of now, these settings are parsed as strings and typos (e.g. a leading space in above example) cannot be detected immediately - in this case the connection to the host would silently fail. We should add a method bool getHost(const std::string & key) const; to "base/poco/Util/include/Poco/Util/AbstractConfiguration.h" which does some basic validity checking by itself and throw an exception accordingly.

[m4xxx1m]

Hi @rschu1ze. I would like to work on this task

[rschu1ze]

@m4xxx1m Happy to hear that. Please ping me for reviews once you have a PR available, thanks!