Allow multi-arch manifest-list from `make container`

[kaovilai]

by changing output type to image.

Then you can execute command like so to create a multi-arch image

BUILDX_PLATFORMS=linux/amd64,linux/arm64 make container

When output type is docker, only single arch is supported and following error is observed.

ERROR: docker exporter does not currently support exporting manifest lists

Signed-off-by: Tiger Kaovilai tkaovila@redhat.com

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[kaovilai]

/kind changelog-not-required

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 59.21%. Comparing base (aab2140) to head (a441687).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #8252 +/- ## ======================================= Coverage 59.21% 59.21% ======================================= Files 367 367 Lines 30841 30841 ======================================= Hits 18262 18262 Misses 11119 11119 Partials 1460 1460 ```

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