### 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/
# apigw
        resps = [
            {
                "statusCode": "204",
                "httpMethod": "OPTIONS",
                "responseParameters": {
                    "method.response.header.Access-Control-Allow-Methods": "'POST,OPTIONS'",
                    "method.response.header.Vary": "'Origin'",
                },
            }
        ]
        api_id = self.create_api_gateway_and_deploy(
            integration_type="MOCK", integration_responses=resps
        )
        url = gateway_request_url(api_id=api_id, stage_name=self.TEST_STAGE_NAME, path="/")
        result = requests.options(url)
        self.assertLess(result.status_code, 400)
        self.assertEqual("Origin", result.headers.get("vary"))
        self.assertEqual("POST,OPTIONS", result.headers.get("Access-Control-Allow-Methods"))
    # =====================================================================
    # Helper methods
    # =====================================================================
    def connect_api_gateway_to_s3(self, bucket_name, file_name, api_id, method):