Add "no-lockfile" as an option to "devcontainer.json" config file

Add a `no-lockfile` option to `devcontainer.json` to disable the generation and validation of `.devcontainer-lock.json`.

For example:

```json
{
"name": "my-devcontainer",
"noLockfile": true
}
```

The CLI already supports:

```bash
devcontainer up --no-lockfile
devcontainer build --no-lockfile
```

However, there is currently no way to configure this behavior directly in `devcontainer.json`.

This is especially problematic when the Dev Container CLI is invoked indirectly by an editor or IDE. In that case, users do not necessarily control the CLI arguments and therefore cannot easily pass `--no-lockfile`.

In my workflow, I intentionally do not want a lockfile. When `.devcontainer-lock.json` is generated or changes, it can cause the environment to be considered out of date and trigger an unnecessary rebuild. Deleting the lockfile allows me to reconnect to the existing container without rebuilding it, but having to manually remove it is a poor workaround.