Github workflow to package and release extension

[anupdhml]

Right now, we locally build the extension package and upload it to vscode marketplace. See if it can be automated fully on releases -- at the very least, we can package the extension and have it be available for download on the releases page.

Current packaging instructtions:
https://github.com/wayfair-tremor/tremor-vscode/blob/master/development.md#packaging

[adithyaakrishna]

@anupdhml @Licenser I would like to work on this 👀