> (you don't have to strictly follow this form)

**Use case**

Sometimes, for really sophisticated scenarios it can be hard to control the amount of in-progress backups run externally. For the purpose of simpler control we can introduce server-level setting which disallows running concurrent backups of any type. 

Something like this in `config.xml` (enabled by default):
`<allow_concurrent_backups>true</allow_concurrent_backups>`

**Describe the solution you'd like**

It's important that backups can be executed in distributed way on multiple servers. Need to take it into account.

**Describe alternatives you've considered**
External check of `system.backups` table, but it can be complex.

{
    Poco::Util::AbstractConfiguration::Keys keys;
    config.keys(config_name, keys);
    for (const auto & key : keys)
    {
        if (startsWith(key, "node"))
        {
            String host = config.getString(config_name + "." + key + ".host");
            if (isLocalAddress(DNSResolver::instance().resolveHost(host)))
                return true;
        }
    }
    return false;
}
}
bool Context::tryCheckClientConnectionToMyKeeperCluster() const