Add opencontainer image spec labels to dockerfile

[ch0wm3in]

Hi,

This commit will add the label ´org.opencontainers.image.source="https://github.com/n8n-io/n8n"´ to the base dockerfile and the ones not extending the former. https://github.com/opencontainers/image-spec/blob/main/annotations.md

The PR will ensure better integration with eg. dependency bots using that piece of information to gather changelog from github to put it into a PR, one such example is renovate https://docs.renovatebot.com/modules/datasource/docker/

The label will extend from the base to the extendees pr label docs https://docs.docker.com/engine/reference/builder/#label

[CLAassistant]

All committers have signed the CLA.

[netroy]

@ch0wm3in This needed to be updated, but Since your branch has push protection enabled, maintainers can't push to it.
I've created a new PR.