Switch from Tekton Hub to Artifacthub in examples and docs.

[twoGiants]

Summary

Switch from Tekton Hub to Artifacthub in examples and a few docs entries as a follow-up to this thread from #8885.

/help
/good-first-issue

[tekton-robot]

@twoGiants:
This request has been marked as suitable for new contributors.

Please ensure the request meets the requirements listed here.

If this request no longer meets these requirements, the label can be removed
by commenting with the /remove-good-first-issue command.

In response to this:

Summary

Switch from Tekton Hub to Artifacthub in examples and a few docs entries as a follow-up to this thread from #8885.

/help
/good-first-issue

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