Add reference to latest Elyra blog post to the documentation

[ptitzler]

This PR adds a ink to the "Customizing Elyra pipelines" blog post to the "Articles, blog posts, and other resources" documentation topic.

The PR will remain in draft until the blog post was published and the static URL is available.

Signed-off-by: Patrick Titzler ptitzler@us.ibm.com

What changes were proposed in this pull request?

See above.

How was this pull request tested?

• Reviewed the output of make docs and verified that the URL does not require a medium.com login.

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