Update and fix OpenFaaS CE

[alexellis]

BACKGROUND

• Add information about the background and reason for the change.

A community user reported that the chart was no longer working on DOKS' marketplace.

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Changes

This change removes the deprecated "src" approach to defining the app, and updates:

• The Helm chart version
• The included versions of software in the README.

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Checklist

• review the contributing doc with steps for both adding or updating your application (if applicable)

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Reviewer: @marketplace-eng

[github-actions]

👋 @alexellis
If this is an EXISTING Marketplace app, now that the PR is merged, all new users of your app will get the current version. You should visit the Vendor Portal to make sure you update any version numbers, Description, or Getting Started information that are related to the merged PR.
If this is a BRAND NEW Marketplace app, before this app update can go live on the Marketplace, please update and submit your app from the Vendor Portal.
Thanks!