Make buildah manifest push --all true by default

[k9withabone]

What type of PR is this?

/kind api-change

/kind bug

/kind cleanup
/kind deprecation
/kind design
/kind documentation
/kind failing-test
/kind feature
/kind flake
/kind other

What this PR does / why we need it:

Changed the --all option of buildah manifest push to be true by default. This matches the behavior of the equivalent Podman option (podman manifest push --all), making it easier to switch between Podman and Buildah.

Updated buildah-manifest-push(1) docs to reflect this change.

How to verify it

Use buildah manifest push --help, see that at the end of the line for the --all it says (default true).

Which issue(s) this PR fixes:

Fixes #5547

Special notes for your reviewer:

Does this PR introduce a user-facing change?

`buildah manifest push --all` is now true by default to match Podman.

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[rhatdan]

Could you Fix the man page and add a tests.

Test could be the equivalent of:

buildah manifest push --help | grep all.*true

[k9withabone]

Added test "manifest-push-all-default-true" to tests/lists.bats.

What's wrong with the man page?

[rhatdan]

Add information about the default being true. Booleans without default in man pages are assumed False.

[k9withabone]

Add information about the default being true.

Already done. It is the same as the Podman man page now.

[rhatdan]

LGTM
@nalind @flouthoc @giuseppe @mheon PTAL