docs: document Kanvas publish-to-catalog flow

[SujalTripathi]

Fixes layer5io/docs#852

This PR adds a short “Publishing from Kanvas” section to the Cloud Catalog docs (content/en/cloud/catalog/_index.md),

documenting how to publish a design from Meshery Kanvas (Playground) into the Cloud Catalog using:

• Open design in Kanvas
• Hamburger menu → Share… → Publish to catalog
• Fill in name, type, description, then click Publish To Catalog

This helps contributors working on Meshery design issues understand how to publish their designs from Playground so they appear in the Cloud Catalog.

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[SujalTripathi]

Signed-off-by: SujalTripathi [email protected]

[SujalTripathi]

Hi @leecalcote please take a look