Ethdoc plugin

[joeizang]

This PR generates documentation from compiled contracts using openzeplin docgen libraries @bunsenstraat adapted for remix ide. Follow these steps to test:

• Checkout this branch locally
• using the NX VsCode plugin, run both docviewer and remixdocgen plugins
• add local iframe plugins for both remixdocgen (sidepanel on localhost:6003) and docviewer (mainPanel on localhost:7003).
• compile any contract and switch to docgen plugin and click on generate (note that this sidepanel UI is very temporary for now) and the docviewer will display the generated documentation.

The docviewer handles the generated md files and displays them. You will find the docs inside the docs folder in File Explorer

fix #3462

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[yann300]

please update the naming of the plugin (the folder name too), this should be doc-viewer and doc-gen