adding --zip/-O flag

[MatthewFletcher]

This is my first Pull Request to a larger project, so please let me know if I'm doing something incorrect!

Fixes #28420

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Does this PR introduce a user-facing change?

podman save now allows for the user to use --zip to directly write to a .tar.gz file instead of having to pipe this into gzip.

Before:

$ podman save imagename:1 | gzip > outfile.tar.gz

Now:

$ podman save --zip imagename:1 > outfile.tar.gz 

(Working on adding a feature to auto-name the output file)

[mheon]

This can be removed

[mheon]

This feels like it should be integrated with the handling of the output flag - right now it feels like it duplicates a lot of that

[Luap99]

Not a proper review but design wise I am not sure why we would call this --zip when it uses gzip. Also generally speaking I am not sure we would want lock us into a specific format like that. Other commands support --compression-format so that seem like a better option to be consistent and support multiple formats.

Then the other thing implementing this here on the client side via pipe adds exactly nothing over just having the user pipe it themselves performance wise so IMO like that there is no benefit on doing this at all.

Instead it would be better IMO to have this compression done server side so in case of podman-remote so we do not have to transfer everything uncompressed. And it would give HTTP API users the option to use it as well. Also when we do it at the source we can directly compress without copying the full stream again through the pipes

[MatthewFletcher]

Part of opening this was to start a discussion on the feasibility of a feature like this. My code in my MR is a proof of concept and I'm absolutely open to ideas on how to make it more compatible with the rest of podman.

This is also my first contribution to a larger project so I'm still learning my way around this.