Add --if-not-exists option to podman network create

[Luap99]

If --if-not-exists is set podman network create will not error
if the a network with the same given name already exists.

This option is only supported for local podman client. Supporting
the remote client would require changes in the api endpoint.

This option can be used as ExecStartPre command in a systemd
service file. see #8842

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[rhatdan]

Bikeshedding a little, but I hate options with "-" embeded in them.

--ignore?
--exists?

[rhatdan]

Currently we have commands

podman image exists
podman pod exists
podman container exists

We should add
podman network exists
podman volume exists
podman manifest exists

Would that be better, then you could make a command like
podman network exists || podman network create ...

[vrothberg]

Container/Pod creation also has a --replace flag which would remove existing objects in case of name conflicts.

[Luap99]

@vrothberg Replace behaviour is not wanted. see #8842

[Luap99]

@rhatdan I agree podman network exists would make sense.

[vrothberg]

+1

[Luap99]

podman network exists PR #9021