For v2 extensions parse entrypoint data

[AshokChoudhary11]

This change will make entrypoint data available for jupyterlab application.
It will be consumed for loading the plugins in a no-code way. Refer https://hackmd.io/DBlDBDszSVSjYK9ieg1mZA

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[fcollonval]

Thanks @AshokChoudhary11

I proposed a simplification.

Could you write down some prose in the PR description to explain why you are proposing this changes and what it adds?

[fcollonval]

Thanks @AshokChoudhary11

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