Add typescript support

[FedeBev]

Hi there, thanks for this great image

Summary

This PR resolves #9 adding typescript support through ts-protoc-gen

Changes

• runtime image is now node-alpine based (node:${NODE_VERSION}-alpine${ALPINE_VERSION}) rather than alpine${ALPINE_VERSION}
• add ts-protoc-gen npm global package
• add ts-protoc-gen to protoc plugins

Notes for Reviewers

I'm aware that changing the final image is not the best but I've chosen to do that because in unfortunately ts-protoc-gen is a node script instead of a runnable binary, therefore node must be installed.
I've tried to install node through apk but the available versions are very limited (the latest version available is nodejs-12.18.4).
I've tried the installation directly with the binary through wget but it didn't work because of a broblem with musl library.
That being said, in my opinion the best option in order to have a stable image is to use the official, alpine-based, node image.
If you think there's a better solution, I'm very open to suggestions and ideas

Release Notes

Despite the final image is changed, this pull request should not contains any breaking change, however I've been able to test only the ts, js and go generation because my current stack contains only this three languages

[rvolosatovs]

Thanks!