example: Use a Redis cacheHandler w/o dependencies

[icyJoseph]

Verify locally:

• Copy the example to a local directory
• Install deps
• docker compose up -d
• npm run build && npm run start
• navigate to localhost:3000/cet (or gmt)
• open the Redis view (link in localhost:3000/cet)
• revalidate data on /cet or /gmt
• verify it on the Redis view

I had to update the app to async params, updateTag, and write the handler in such a way that it solved:

⨯ TypeError: p.segmentData.get is not a function
    at ignore-listed frames
⨯ Error: failed to pipe response

Also adding docs edits with this caveat.

An agent review, and cross checking with a community implementation, surfaced, that we had to read tags from data.headers['x-next-cache-tags']. This agent review added a few comments, I think they are useful, but can cut down if needed.

Last but not least, had to update the Time API endpoint (former no longer worked).

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