### Is there an existing issue for this?

- [X] I have searched the existing issues

### Feature description

I prefer not to use the real regions when doing tests or local stuff to make sure that if it accidentally picks up real credentials, it won't actually create or interact with resources in AWS. This used to work find in localstack - I even dug through the code to find that there is an option in the `RegionStore` to disable validation of the region string. At some point, you removed any way to disable that validation though, which means it just fails all requests using a custom region.

### 🧑‍💻 Implementation

There's already a flag that is passed to the account and region store constructors to disable validation. Seems like an environment variable or configuration flag to disable validation could be propagated.

### Anything else?

_No response_
return "https" if USE_SSL else "http"
def service_url(service_key, host=None, port=None):
    host = host or LOCALHOST
    port = port or service_port(service_key)
    return f"{get_protocol()}://{host}:{port}"
def external_service_url(service_key, host=None, port=None):
    host = host or HOSTNAME_EXTERNAL
    port = port or service_port(service_key, external=True)
    return service_url(service_key, host=host, port=port)
def get_edge_port_http():
    return EDGE_PORT_HTTP or EDGE_PORT
def get_edge_url(localstack_hostname=None, protocol=None):
    port = get_edge_port_http()
    protocol = protocol or get_protocol()
    localstack_hostname = localstack_hostname or LOCALSTACK_HOSTNAME
    return "%s://%s:%s" % (protocol, localstack_hostname, port)
def edge_ports_info():
    if EDGE_PORT_HTTP:
        result = "ports %s/%s" % (EDGE_PORT, EDGE_PORT_HTTP)
    else:
        result = "port %s" % EDGE_PORT
    result = "%s %s" % (get_protocol(), result)
    return result
class ServiceProviderConfig(Mapping[str, str]):