Nested map merge for_each

Terraform
1

Good afternoon. I am looking to create a data structure to create azure route entries.

This map contains all the default rules that get added to every route table:

spoke_template = {
    route_entries = {
        blackhole_mgmt = {
            name             = "BlackholeManagement"
            prefix           = "10.121.0.0/28"
            next_hop_type    = "None"
        }
        blackhole_untrust = {
            name             = "BlackholeUntrust"
            prefix           = "10.121.0.16/28"
            next_hop_type    = "None"
        }
        blackhole_trust_ext = {
            name             = "BlackholeTrustExt"
            prefix           = "10.121.0.48/28"
            next_hop_type    = "None"
        }
        blackhole_fwHA = {
            name             = "BlackholefwHA"
            prefix           = "10.121.0.64/28"
            next_hop_type    = "None"
        }
        blackhole_app_gwy = {
            name             = "BlackholeAppGateway"
            prefix           = "10.121.0.128/25"
            next_hop_type    = "None"
        }
        rfc-1918-10 = {
            name             = "RFC-1918-10"
            prefix           = "10.0.0.0/8"
            next_hop_type    = "VirtualAppliance"
            next_hop_type_ip = "10.121.0.36"
        }
        rfc-1918-172 = {
            name             = "RFC-1918-172"
            prefix           = "172.16.0.0/12"
            next_hop_type    = "VirtualAppliance"
            next_hop_type_ip = "10.121.0.36"
        }
        rfc-1918-192 = {
            name             = "RFC-1918-192"
            prefix           = "192.168.0.0/16"
            next_hop_type    = "VirtualAppliance"
            next_hop_type_ip = "10.121.0.36"
        }
        default-route = {
            name             = "default"
            prefix           = "0.0.0.0/0"
            next_hop_type    = "VirtualAppliance"
            next_hop_type_ip = "10.121.0.50"
        }
    }
}

This map defines the vnets, subnets, and per-subnet routes:

spokes = {
    vnet-app1-it-dev-use2-001 = {
        resource_group_name = "rg-app1-net-it-dev-use2"
        sn-web-dev = {
            route_entries = {
                intra-subnet = {
                    name             = "Intra-VNet"
                    prefix           = "10.121.96.0/28" # Dynamic
                    next_hop_type    = "VirtualAppliance"
                    next_hop_type_ip = "10.121.0.36"
                }
                intra-vnet = {
                    name             = "Intra-VNet"
                    prefix           = "10.121.96.0/24" # Dynamic
                    next_hop_type    = "VirtualAppliance"
                    next_hop_type_ip = "10.121.0.36"
                }
            }
        }
        sn-app-dev = {
            route_entries = {
                intra-subnet = {
                    name             = "Intra-VNet"
                    prefix           = "10.121.96.16/28"
                    next_hop_type    = "VirtualAppliance"
                    next_hop_type_ip = "10.121.0.36"
                }
                intra-vnet = {
                    name             = "Intra-VNet"
                    prefix           = "10.121.96.0/24"
                    next_hop_type    = "VirtualAppliance"
                    next_hop_type_ip = "10.121.0.36"
                }
            }
        }
        sn-db-dev = {
            route_entries = {
                intra-subnet = {
                    name             = "Intra-VNet"
                    prefix           = "10.121.96.32/28"
                    next_hop_type    = "VirtualAppliance"
                    next_hop_type_ip = "10.121.0.36"
                }
                intra-vnet = {
                    name             = "Intra-VNet"
                    prefix           = "10.121.96.0/24"
                    next_hop_type    = "VirtualAppliance"
                    next_hop_type_ip = "10.121.0.36"
                }
            }
        }
    }
}

Ideally, I would like to loop the spokes map and add the spoke_template map route_entries along with the custom route entries in the spokes map. I am unsure of the proper way to design the maps so that I can loop and merge them. Any help would be greatly appreciated. Thanks.