Fix invalid KFP component URL references

[ptitzler]

Closes #2502

What changes were proposed in this pull request?

Update all invalid GitHug resource URL with a valid one.

How was this pull request tested?

Reviewed the output of make docs and confirmed that the displayed GitHub URLs are valid

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[kiersten-stokes]

LGTM! Links are working

[lresende]

Why do we have airflow in the main repo, and kfp is in the example one?

[ptitzler]

Why do we have airflow in the main repo, and kfp is in the example one?

Not sure I understand your question. The documentation contained example CLI invocations that include references to KFP example component definitions. In older releases those component definitions used to live in the elyra repo, but they no longer do. The same is true for Airflow. All example components are stored in https://github.com/elyra-ai/examples/tree/master/component-catalog-connectors. This PR only updates the incorrect links.