Cleanup plugin registry by removing editors

[svor]

Is your task related to a problem? Please describe

The task is about removing a few things related to Che editors:

• che-editors.yaml file that contains editors definitions.
• The tool that generates editors from che-editors.yaml.
• Cleanup GH actions that publish editors definitions
• Update README.md and CONTRIBUTE.md files

The same procedure should be done in downstream: https://github.com/redhat-developer/devspaces/tree/devspaces-3-rhel-8/dependencies/che-plugin-registry. Downstream uses the tool to generate editors definitions in this script: https://github.com/redhat-developer/devspaces/blob/devspaces-3-rhel-8/dependencies/che-plugin-registry/build.sh#L235

This task is a continuation of Decouple editor definitions from the plugin registry #22932. Also it should be done after Deprecate and archive che-devfile-registry #22960, because devfile registry uses published editors to generate DevWorkspaceTemplate objects: https://github.com/eclipse-che/che-devfile-registry/blob/main/build/scripts/generate_devworkspace_templates.sh#L21 and https://github.com/redhat-developer/devspaces/blob/devspaces-3-rhel-8/dependencies/che-devfile-registry/build/scripts/generate_devworkspace_templates.sh#L39-L65

[che-bot]

Issues go stale after 180 days of inactivity. lifecycle/stale issues rot after an additional 7 days of inactivity and eventually close.

Mark the issue as fresh with /remove-lifecycle stale in a new comment.

If this issue is safe to close now please do so.

Moderators: Add lifecycle/frozen label to avoid stale mode.