docs: use computed property value in docs

[femioladipo]

What?

Refactor storage adapter collections config in the examples to use computed property values via .slug rather than raw string literals.

Why?

Using computed values (e.g., [Media.slug]) ensures the adapter key stays in sync with the actual collection slug, avoiding silent mismatches due to typos or future refactors. While such mismatches shouldn’t happen in a well-managed codebase, “Anything that can happen will happen.” – Murphy’s Law.

This approach improves reliability and clarity. The original example mixed media (default collection key) with a literal string 'media-with-prefix', which could be confusing—especially since these examples are in documentation and readers cannot inspect the underlying collections directly to understand these are representing their respective slugs.

How?

Replaced hard-coded keys in the collections config with computed property values:

collections: {
  [Media.slug]: true,
  [MediaWithPrefix.slug]: { prefix },
}

This ensures both configuration keys are explicitly tied to their respective collections.