This is a redux of #30588 rebased and after the repo move!

- What I did

Added a mechanism to allow HTTP/HTTPS/FTP/NO proxy variables to be configured in config.json. These are then automatically populated in a docker run command as environment variables or as build-args in docker build!

This makes it easier for users suffering behind an HTTP Proxy as they only need to configure this once as opposed to creating custom aliases or forgetting the args and being denied buildage/runnage.

Updates #30323

- How I did it

Extended the configfile with some new proxy related variables.

These are scoped per Docker Host with a default catchall.

The config file is then read by the build or run command and the necessary variables are exported.

A -e flag or --build-arg provided on the CLI will override these default settings.

- How to verify it

There are integration tests! But manually, you may:

1. Create a config.json with { "proxies" : { "httpProxy" : "http://127.0.0.1:3001" }
2. Create a Dockerfile

FROM busybox
RUN echo $HTTP_PROXY
CMD echo $HTTP_PROXY

3. docker --config /path/to/config build -t configtest .
4. Verify that the HTTP_PROXY variable is as configured
5. docker run --rm configtest env
6. Verify that the HTTP_PROXY variable is as configured

- Description for the changelog

Added HTTP/HTTPS/FTP proxy configuration to config.json

- A picture of a cute animal (not mandatory but encouraged)