skupper init improve help text

[Karen-Schoener]

Improve help text in skupper init if podman endpoint is not available.

Fixes #1471

[Karen-Schoener]

Test case: run as root:

[root@fedora skupper]# ./skupper --platform podman init
Podman endpoint is not available: unix:///run/podman/podman.sock

Recommendation:

        Make sure you have an active podman endpoint available.
        On most systems you can execute:

                systemctl enable --now podman.socket

        Alternatively you could also create your own service that runs:

                podman system service --time=0 <URI>

        You can get concrete examples through:

                podman help system service

Test case: run as non-root:

[kschoener@fedora skupper]$ ./skupper --platform podman init
Podman endpoint is not available: unix:///run/user/1000/podman/podman.sock

Recommendation:

        Make sure you have an active podman endpoint available.
        On most systems you can execute:

                systemctl --user enable --now podman.socket

        Alternatively you could also create your own service that runs:

                podman system service --time=0 <URI>

        You can get concrete examples through:

                podman help system service