fix(www): use the stackblitz examples

[timdeschryver]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/ngrx/platform/blob/main/CONTRIBUTING.md#commit
• Tests for the changes have been added (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

[x] Bugfix
[ ] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Build related changes
[ ] CI related changes
[ ] Documentation content changes
[ ] Other... Please describe:

What is the current behavior?

The stackblitz examples are not rendered.

Closes #4878

What is the new behavior?

The examples are rendered, either via a link or embedded.

Does this PR introduce a breaking change?

[ ] Yes
[x] No

Other information

We should port over the examples to www, and migrate the examples to use the stackblitz SDK.
For the store examples, we should update the docs to go with the new example.
For example, there's no app subfolder anymore, and we don't make use of a Module anymore.
The other examples should probably also me rewritten for the standalone api.

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