auth-proxy: configurable upstream proxy via env vars #1117

Job	Run time
test-make-all (podman, ubuntu-24.04)	8m 26s
test-make (acng, podman, ubuntu-24.04)	48s
test-compose (test_compose_run, ubuntu-24.04)	6m 8s
test-make (auth_proxy, podman, ubuntu-24.04)	1m 0s
docker-buildx (auth-proxy, imags/git-auth-proxy/Dockerfile, imags/git-auth-proxy, localhost/l7/au...	1m 20s
test-compose (images_gui, ubuntu-24.04)	8m 13s
test-make (container_proxy, podman, ubuntu-24.04)	37s
docker-buildx (container-socket-proxy, imags/container-socket-proxy, imags/container-socket-proxy...	52s
test-e2e-podman (curl, 24.04)	7m 17s
test-make (caddy, podman, ubuntu-24.04)	2m 9s
docker-buildx (dnsmasq, imags/dnsmasq/Containerfile, imags/dnsmasq, localhost/l7/dnsmasq:latest)	26s
test-make (dnsmasq, podman, ubuntu-24.04)	23s
test-e2e-podman (ghauth, 24.04)	6m 29s
docker-buildx (gpg-vault, imags/gpg-vault-pk/Containerfile, ., localhost/l7/gpg-vault:latest)	38s
test-make (gpg_pk, podman, ubuntu-24.04)	29s
test-e2e-podman (node_corepack, 24.04)	6m 21s
docker-buildx (node, imags/node-runner/Containerfile, ., localhost/l7/node:latest localhost/l7/no...	4m 11s
test-make (nvim, podman, ubuntu-24.04)	7m 47s
test-e2e-podman (lsp_typescript, 24.04)	7m 50s
test-make (runner_node, podman, ubuntu-24.04)	2m 52s
docker-buildx (nvim, imags/nvim/Containerfile, ., localhost/l7/nvim:latest localhost/l7/dev-shell...	3m 0s
test-e2e-podman (node_majors, 24.04)	8m 34s
	1h 25m 50s

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