### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

When creating base-path-mappings on an API Gateway, there is a special `(none)` path when you don't specify a path during creation. Localstack stores this as `basePath: "(none)"` internally.
When you query to get the base paths, the URLs are escaped by the client (verified in both awscli and terraform) so the basePath is sent as `%28none%29` in the url.
Localstack doesn't appear to be decoding urls and when you attempt to get-base-path-mapping it fails in a string comparison of `(none)` to `%28none%29`.

```shell
> aws --endpoint-url=http://localhost:4566 apigateway get-base-path-mapping --domain-name example.com --base-path "(none)"

An error occurred (NotFoundException) when calling the GetBasePathMapping operation: Base path mapping not found: %28none%29
```

### Expected Behavior

When you attempt to get-base-path-mappings after creating one with the (none) path, it succeeds and returns the mapping.

```
> aws --endpoint-url=http://localhost:4566 apigateway get-base-path-mapping --domain-name example.com --base-path "(none)"

{
    "basePath": "(none)",
    "restApiId": "uyy4c3dsho",
    "stage": "dev"
}
```


### How are you starting LocalStack?

With the `localstack` script

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    make start

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    awslocal apigateway create-rest-api --name "testgw"
    awslocal apigateway create-base-path-mapping --domain-name example.com --rest-api-id <from output above> --stage dev
    awslocal apigateway get-base-path-mapping --domain-name example.com --base-path "(none)"



### Environment

```markdown
- OS: fedora 34
- LocalStack: latest
```


### Anything else?

https://docs.aws.amazon.com/apigateway/api-reference/link-relation/basepathmapping-by-base-path/
return to_response_json("documentationpart", data, api_id=api_id)
def to_base_mapping_response_json(domain_name, base_path, data):
    self_link = "/domainnames/%s/basepathmappings/%s" % (domain_name, base_path)
    return to_response_json("basepathmapping", data, self_link=self_link)
def to_account_response_json(data):
    return to_response_json("account", data, self_link="/account")
def to_vpc_link_response_json(data):
    return to_response_json("vpclink", data)
def to_client_cert_response_json(data):
    return to_response_json("clientcertificate", data, id_attr="clientCertificateId")
def to_response_json(model_type, data, api_id=None, self_link=None, id_attr=None):
    if isinstance(data, list) and len(data) == 1:
        data = data[0]
    id_attr = id_attr or "id"
    result = common.clone(data)
    if not self_link:
        self_link = "/%ss/%s" % (model_type, data[id_attr])
        if api_id:
            self_link = "/restapis/%s/%s" % (api_id, self_link)
    if "_links" not in result:
        result["_links"] = {}
    result["_links"]["self"] = {"href": self_link}
    result["_links"]["curies"] = {
        "href": "https://docs.aws.amazon.com/apigateway/latest/developerguide/restapi-authorizer-latest.html",
        "name": model_type,
        "templated": True,
    }
    result["_links"]["%s:delete" % model_type] = {"href": self_link}
    return result
def find_api_subentity_by_id(api_id, entity_id, map_name):