Update SSR and transformIndexHtml examples and documentation

[benmccann]

Clear and concise description of the problem

The SSR examples in playground don't set spa: false nor does the SSR documentation demonstrate it

transformIndexHtml is not called when spa: false. It's not very useful as a build hook most of the time in SSR apps because the page contents aren't generated until SSR at runtime

Suggested solution

Update docs and examples

Alternative

No response

Additional context

spa: false was added in #7665

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

[benmccann]

This may change as the result of #8452