Support calculating bucket_id based on ddl.sharding_key

[sharonovd]

Crud/ddl/migrations is a way to go for our customers. But project after a project I observe the following clutches:

local function get_object_by_pk(part1, part2)    
    local bucket_id = vshard.router.bucket_id_mpcrc32(part2)    
    local settings, err_settings = crud.get('object', {part1, part2}, {bucket_id = bucket_id})   
    if err_settings ~= nil then return nil, err_settings    end    
    return settings
end

local function upsert_object(object)    
    local id = settings["id"]    
    local bucket_id = vshard.router.bucket_id_mpcrc32(id)
    local res, err = crud.replace_object("settings_object", settings, {bucket_id = bucket_id})    
    if err ~= nil then        return nil, err    end    
end

But this info is already present in ddl! (ddl.register_sharding_key('object', {"id"}))
This shoould work out-of-the-box