Add helper script and integrate with ssh-agent

[amsobr]

Added a script, poky-container, which can be used to simplify the listing and launching of the available containers.

Listing available containers

Note: the list of containers is maintained by hand.

 poky-container list
AlmaLinux:
    alma-8 alma-9

CentOS:
    centos-7

Debian:
    debian-9 debian-10 debian-11

Fedora:
    fedora-33 fedora-34 fedora-35 fedora-36

OpenSuse:
    opensuse-15.2 opensuse-15.3 opensuse-15.4

Ubuntu:
    ubuntu-16.04 ubuntu-18.04 ubuntu-20.04 ubuntu-22.04

Launching a container

user@host$ poky-container run ubuntu-20.04
...
pokyuser@4da677d43c61:/workdir$ 

Basic help

user@host$ poky-container help
Usage:
    poky-container list
                List available images

    poky-container run IMAGE [HOST_WORKDIR]
                Run the selected image on a specific location

Parameters:
    IMAGE           The name of the image to run
    HOST_WORKDIR    The working directory, ie, location if the workspace
                    on the host, which will show as /workdir in the
                    container.
                    By default, the current working directory is used.

ssh-agent integration

When launching the container, if SSH_AUTH_SOCK is set, the socket is bind-mounted in the container too and ~/.bashrc in the container recreates the SSH_AUTH_SOCK variable.

Feel free to pick any of the changes or suggest improvements.
Thanks.