Core: Improve framework field validation

[yannbf]

Closes #20651

What I did

The framework field is not validated in three different steps:

1. Is there no framework field? -> throw error, tell user to run automigrate
2. Is it a renderer package? -> throw error, tell user to run automigrate
3. Is it a known framework package? -> all good
4. Is it neither of the above? Does the package at least get resolved? else throw error

How to test

1. Run a sandbox for template, e.g. yarn task --task sandbox --start-from auto --template react-vite/default-ts
2. Change the framework field to:
   scenario 1: remove framework field
   scenario 2: framework field value: @storybook/react-vite
   scenario 3: framework field value: react
   scenario 4: framework field value: foo

Checklist

• Make sure your changes are tested (stories and/or unit, integration, or end-to-end tests)
• Make sure to add/update documentation regarding your changes
• If you are deprecating/removing a feature, make sure to update
  MIGRATION.MD

Maintainers

• If this PR should be tested against many or all sandboxes,
  make sure to add the ci:merged or ci:daily GH label to it.
• Make sure this PR contains one of the labels below.

["cleanup", "BREAKING CHANGE", "feature request", "bug", "documentation", "maintenance", "dependencies", "other"]

[shilman]

Generally looks good. Have a couple suggested improvements

[ndelangen]

AFAIK this is not something we allow/support.
The UI will show you a "empty storybook" warning if you'd do that.