podman diff accept two images or containers

[Luap99]

First, make podman diff accept optionally a second argument. This allows
the user to specify a second image/container to compare the first with.
If it is not set the parent layer will be used as before.

Second, podman container diff should only use containers and podman
image diff should only use images. Previously, podman container diff
would use the image when both an image and container with this name
exists.

To make this work two new parameters have been added to the api. If they
are not used the previous behaviour is used. The same applies to the
bindings.

Fixes #10649

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[infiniteregrets]

Thanks @Luap99, I kind of understood where I was going wrong.
Can you add this table to docs for image diff:

The output is prefixed with the following symbols:

| Symbol | Description |
|--------|-------------|
| A | A file or directory was added. |
| D | A file or directory was deleted. |
| C | A file or directory was changed. |

[Luap99]

@infiniteregrets I added this all three diff man pages.

[infiniteregrets]

Looks good!

[mheon]

If this is a bitfield, it seems like it would be better to manually specify - 0b1, 0b10, etc.

[Luap99]

1 << iota is basically just saying to shift the bit one step for each entry. It should be less error prone than writing this manually especially when you add new entries, However I understand that this syntax is confusing if you are not familiar with it. I can remove it if you want.

[mheon]

One nit otherwise LGTM

[baude]

/hold
/lgtm

[Luap99]

I had to repush to fix a test.

[TomSweeneyRedHat]

/lgtm

[rhatdan]

/hold cancel