Support for modifing the platform and framework in GUI

### Before opening, please confirm:

- [X] I have checked to see if my question is addressed in the [FAQ](https://github.com/aws-amplify/amplify-hosting/blob/master/FAQ.md).
- [X] I have [searched for duplicate or closed issues](https://github.com/aws-amplify/amplify-hosting/issues?q=is%3Aissue+).
- [X] I have removed any sensitive information from my code snippets and submission.

### Amplify Hosting feature

Build settings

### Is your feature request related to a problem? Please describe:

It would be great if the settings for “Framework” and “Platform” under “App settings -> General settings” could be changed via the GUI. As it stands, I understand that these can only be modified through the AWS CLI.
https://awscli.amazonaws.com/v2/documentation/api/latest/reference/amplify/update-app.html
https://awscli.amazonaws.com/v2/documentation/api/latest/reference/amplify/update-branch.html


### Describe how you'd like this feature to work

no image

Review the Amplify Hosting build-settings area under App settings > General settings, then compare its current controls with the AWS CLI update-app and update-branch documentation linked in the issue. Done means users can modify both Framework and Platform through the GUI and those changes are persisted.

Written by the indexing model from the issue text.