Improved CSP documentation

[benmccann]

Describe the problem

%svelte.nonce% does not appear to be documented anywhere

Also, we don't really describe what happens with the various options. E.g. what happens if you set hash? It's a lesser issue, but we could possibly illuminate it a little more

Describe the proposed solution

I assume we'd like to document it?

Alternatives considered

No response

Importance

nice to have

Additional Information

No response

[Mlocik97]

So the same as #2035

in docs, whole %svelte.<something>% stuffs are missing.

[PlopTheReal]

I was wondering if that would solve the following : #5724

[CanRau]

found in the docs by searching for nonce https://kit.svelte.dev/docs/project-structure#project-files-src

though still not sure how to solve #5724