chore: stop using Che plugin registry for editor definitions

[svor]

What does this PR do?

• Stop using che-plugin-registry URL to get editor definitions, instead it's possible to provide editorURL parameter
• Add .devfile.yaml to develop on Che
• Add LICENSE file
• Update README
• Add default extensions

What issues does this PR fix or reference?

eclipse-che/che#23187

Is it tested? How?

It could be tested by running it on Che instance using factory:

And execute commands provided by devfile:

• Build
• Generate DevWorkspace with Template (it uses editorURL as a prameter)

As a result /tmp/devworkspace-che-code-latest.yaml should be generated

[svor]

cc @musienko-maxim

[svor]

@olexii4 @RomanNikitenko FYI
che-dashboard and che-code may be affected when the devworkspace-generator version is updated

[openshift-ci]

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This pull-request has been approved by: svor, tolusha

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