> (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.

{
    auto lock = getLock();
    auto profile_info = getAccessControl().getSettingsProfileInfo(profile_id);
    checkSettingsConstraints(profile_info->settings);
    applySettingsChanges(profile_info->settings);
    settings_constraints_and_current_profiles = profile_info->getConstraintsAndProfileIDs(settings_constraints_and_current_profiles);
}
std::vector<UUID> Context::getCurrentProfiles() const
{
    auto lock = getLock();
    return settings_constraints_and_current_profiles->current_profiles;
}
std::vector<UUID> Context::getEnabledProfiles() const
{
    auto lock = getLock();
    return settings_constraints_and_current_profiles->enabled_profiles;
}
ResourceManagerPtr Context::getResourceManager() const