Request: option to disable mounts.

Hi folks, I had a situation in which the mount broke my pipeline. I'm currently doing a read only bind of ~/.ssh and mounting a volume that is used for storing the cli history... when I try to build it in AzDO it fails saying that there is no .ssh ... that is expected ... is there a way to disable mounts?

Saw it was including in issue #30

```bash
docker: Error response from daemon: invalid mount config for type "bind": bind source path does not exist: /home/vsts/.ssh.
```
Can't see this [line](https://github.com/devcontainers/ci/blob/afa58a5848bbf08f67d2a6be8935cf8121802362/common/src/docker.ts#L286) in the logs.

cheers,

Juan