### 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_
or "domain"
)
if OPENSEARCH_ENDPOINT_STRATEGY == "off":
    OPENSEARCH_ENDPOINT_STRATEGY = "port"
OPENSEARCH_MULTI_CLUSTER = is_env_not_false("OPENSEARCH_MULTI_CLUSTER") or is_env_true(
    "ES_MULTI_CLUSTER"
)
CONFIG_ENV_VARS = [
    "BUCKET_MARKER_LOCAL",
    "DEBUG",
    "DEFAULT_REGION",
    "DEVELOP",
    "DEVELOP_PORT",
    "DISABLE_CORS_CHECKS",
    "DISABLE_CORS_HEADERS",
    "DISABLE_CUSTOM_CORS_APIGATEWAY",
    "DISABLE_CUSTOM_CORS_S3",
    "DISABLE_EVENTS",
    "DOCKER_BRIDGE_IP",
    "DYNAMODB_ERROR_PROBABILITY",
    "DYNAMODB_HEAP_SIZE",
    "DYNAMODB_SHARE_DB",
    "DYNAMODB_READ_ERROR_PROBABILITY",
    "DYNAMODB_WRITE_ERROR_PROBABILITY",
    "EAGER_SERVICE_LOADING",
    "EDGE_BIND_HOST",
    "EDGE_FORWARD_URL",
    "EDGE_PORT",
    "EDGE_PORT_HTTP",
    "ENABLE_CONFIG_UPDATES",