add initial xonsh shell support - close #175 #369

Job	Run time
fresh-macos-test	5m 5s
homebrew-macos-test	5m 4s
login-shells-and-linting	5m 5s
distro-test (ubuntu:latest)	2m 58s
distro-test (fedora:latest)	3m 44s
distro-test (debian:latest)	3m 6s
distro-test (alpine:latest)	4m 55s
distro-test (manjarolinux/base)	2m 50s
distro-test (opensuse/leap)	4m 53s
distro-test (opensuse/tumbleweed)	3m 7s
distro-test (kalilinux/kali-rolling)	3m 4s
distro-test (voidlinux/voidlinux)	3m 22s
	47m 13s

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