> (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.

{
    return getAccess()->getRolesInfo();
}
void Context::calculateAccessRights()
{
    auto lock = getLock();
    if (user_id)
        access = getAccessControl().getContextAccess(
            *user_id,
            current_roles ? *current_roles : std::vector<UUID>{},
             false,
            settings,
            current_database,
            client_info);
}
template <typename... Args>
void Context::checkAccessImpl(const Args &... args) const
{
    return getAccess()->checkAccess(args...);
}
void Context::checkAccess(const AccessFlags & flags) const { return checkAccessImpl(flags); }
void Context::checkAccess(const AccessFlags & flags, std::string_view database) const { return checkAccessImpl(flags, database); }
void Context::checkAccess(const AccessFlags & flags, std::string_view database, std::string_view table) const { return checkAccessImpl(flags, database, table); }
void Context::checkAccess(const AccessFlags & flags, std::string_view database, std::string_view table, std::string_view column) const { return checkAccessImpl(flags, database, table, column); }
void Context::checkAccess(const AccessFlags & flags, std::string_view database, std::string_view table, const std::vector<std::string_view> & columns) const { return checkAccessImpl(flags, database, table, columns); }
void Context::checkAccess(const AccessFlags & flags, std::string_view database, std::string_view table, const Strings & columns) const { return checkAccessImpl(flags, database, table, columns); }
void Context::checkAccess(const AccessFlags & flags, const StorageID & table_id) const { checkAccessImpl(flags, table_id.getDatabaseName(), table_id.getTableName()); }