Error when clicking Run Space from a space settings page when a custom image is pre-selected

### Product Version

- [ ] Amazon SageMaker Studio Classic
- [X] Amazon SageMaker Studio
- [ ] Issue is not related to SageMaker Studio

### Issue Description

There's an unhandled error upon clicking Run Space when following these steps:

2. Select a custom image in a JuypterLab space
3. Refresh or navigate away and return
4. Press Run Space

### Expected Behavior

Space starts

### Observed Behavior

400 error with following message:

```
2 validation errors detected: Value '' at 'spaceSettings.jupyterLabAppSettings.defaultResourceSpec.sageMakerImageVersionAlias' failed to satisfy constraint: Member must satisfy regular expression pattern: (^\\d+$)|(^\\d+.\\d+$)|(^(0|[1-9]\\d*)\\.(0|[1-9]\\d*)\\.(0|[1-9]\\d*)(?:-((?:0|[1-9]\\d*|\\d*[a-zA-Z-][0-9a-zA-Z-]*)(?:\\.(?:0|[1-9]\\d*|\\d*[a-zA-Z-][0-9a-zA-Z-]*))*))?(?:\\+([0-9a-zA-Z-]+(?:\\.[0-9a-zA-Z-]+)*))?$); Value '' at 'spaceSettings.jupyterLabAppSettings.defaultResourceSpec.sageMakerImageVersionAlias' failed to satisfy constraint: Member must have length greater than or equal to 1"
__type
:
"ValidationException"
```

### Product Category

JupyterLab

### Feedback Category

User Interface

### Other Details

This is due to the preselected value not properly propagating from the UI to the request that is being made.

No source files or tests are identified in the issue. Start by reproducing the JuypterLab space workflow with a custom image, refresh or leave and return to the settings page, then click Run Space and inspect the request containing sageMakerImageVersionAlias. Done means the selected image value reaches the request and the space starts without the 400 validation error.

Written by the indexing model from the issue text.