### 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/
expected = custom_result if int_type == "custom" else "{}"
        self.assertEqual(expected, json.loads(to_str(result.content))["data"])
        
        data = json.dumps({"data": 123})
        result = requests.post(url, data=data)
        self.assertEqual(200, result.status_code)
        expected = custom_result if int_type == "custom" else data
        self.assertEqual(expected, json.loads(to_str(result.content))["data"])
        
        data = "test=123"
        ctype = "application/x-www-form-urlencoded"
        result = requests.post(url, data=data, headers={"content-type": ctype})
        self.assertEqual(200, result.status_code)
        content = json.loads(to_str(result.content))
        headers = CaseInsensitiveDict(content["headers"])
        expected = custom_result if int_type == "custom" else data
        self.assertEqual(expected, content["data"])
        self.assertEqual(ctype, headers["content-type"])
        
        config.DISABLE_CUSTOM_CORS_APIGATEWAY = old_config
        proxy.stop()
    def test_api_gateway_lambda_proxy_integration(self):
        self._test_api_gateway_lambda_proxy_integration(
            self.TEST_LAMBDA_PROXY_BACKEND, self.API_PATH_LAMBDA_PROXY_BACKEND
        )
    def test_api_gateway_lambda_proxy_integration_with_path_param(self):
        self._test_api_gateway_lambda_proxy_integration(
            self.TEST_LAMBDA_PROXY_BACKEND_WITH_PATH_PARAM,
            self.API_PATH_LAMBDA_PROXY_BACKEND_WITH_PATH_PARAM,
        )