We need to drop node 16 support, [as support for it is ends much earlier now, due to support for openssl 1.1.1 ending](https://nodejs.org/en/blog/announcements/nodejs16-eol).
`0.236.x` releases will continue to support Node.js 16 for another two months, and `1.x.x` releases will only support Node.js 18 for now.
* ci: Remove debian and rhel7 images
* include libc6-compat in all alpine images
* run all n8n docker containers as the user `node` instead of `root`
* upgrade the default version of npm bundled in all containers
* consolidate docker entrypoints
* reduce redundant code between the two alpine Dockerfiles
* reduce the docker image build times
* reduce the `n8n` image size from 1.17GB to 462MB
* reduce the `n8n-custom` image size from 671MB to 460MB
* reduce the size of npm tree by making all typing packages devDependencies
Partially resolves this ticket: N8N-3252
