### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

There's no way to explicitly toggle the `-inMemory` flag for DynamoDB - it relies on [`db_path` being unset](https://github.com/localstack/localstack/blob/v1.0.1/localstack/services/dynamodb/server.py#L45). However, `db_path` is always set because it [relies on config.dirs.data](https://github.com/localstack/localstack/blob/v1.0.1/localstack/services/dynamodb/server.py#L107-L113), which is [always set](https://github.com/localstack/localstack/blob/v1.0.1/localstack/config.py#L119).

### Expected Behavior

Maybe have an explicit env var like `DYNAMODB_IN_MEMORY` to force `-inMemory` mode or fix the path based logic in which it can be enabled.

Use case: I'm running tests on an ephemeral localstack container and don't need persistence. I think I'm experiencing the performance hit in https://github.com/localstack/localstack/issues/1205 and `-inMemory` seems be significantly faster.

### How are you starting LocalStack?

With a docker-compose file

### Steps To Reproduce

`docker-compose.yml`
```yaml
version: '3.8'
services:
  localstack:
    image: localstack/localstack:1.0
    environment:
      - EDGE_PORT=4566
      - EAGER_SERVICE_LOADING=1
      - SERVICES=dynamodb
      - PERSISTENCE=0
```

```
$ docker-compose up
...
localstack_1      | 2022-07-23T05:27:50.506  INFO --- [   Thread-12] l.services.dynamodb.server : Initializing DynamoDB Local with the following configuration:
localstack_1      | 2022-07-23T05:27:50.506  INFO --- [   Thread-12] l.services.dynamodb.server : Port:	34585
localstack_1      | 2022-07-23T05:27:50.506  INFO --- [   Thread-12] l.services.dynamodb.server : InMemory:	false
localstack_1      | 2022-07-23T05:27:50.506  INFO --- [   Thread-12] l.services.dynamodb.server : DbPath:	/var/lib/localstack/tmp/state/dynamodb
localstack_1      | 2022-07-23T05:27:50.506  INFO --- [   Thread-12] l.services.dynamodb.server : SharedDb:	false
localstack_1      | 2022-07-23T05:27:50.506  INFO --- [   Thread-12] l.services.dynamodb.server : shouldDelayTransientStatuses:	false
localstack_1      | 2022-07-23T05:27:50.506  INFO --- [   Thread-12] l.services.dynamodb.server : CorsParams:	*
...
```

### Environment

```markdown
- OS: Docker on Mac M1
- LocalStack: 1.0.1
```


### Anything else?

_No response_
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]):
    _provider_config: Dict[str, str]
    default_value: str
    override_prefix: str = "PROVIDER_OVERRIDE_"
    def __init__(self, default_value: str):
        self._provider_config = {}
        self.default_value = default_value
    def load_from_environment(self, env: Mapping[str, str] = None):
        if env is None:
            env = os.environ
        for key, value in env.items():
            if key.startswith(self.override_prefix):
                self.set_provider(key[len(self.override_prefix) :].lower().replace("_", "-"), value)
    def get_provider(self, service: str) -> str:
        return self._provider_config.get(service, self.default_value)
    def set_provider_if_not_exists(self, service: str, provider: str) -> None: