fix: use Docker Buildx for multi-arch CI builds

[rollandf]

Use docker/build-push-action with QEMU and Buildx to handle multi-arch builds automatically, eliminating manifest creation errors.

[coveralls]

Pull Request Test Coverage Report for Build 19745268962

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 6 unchanged lines in 2 files lost coverage.
• Overall coverage increased (+0.2%) to 62.242%

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Files with Coverage Reduction	New Missed Lines	%
controllers/ipoibnetwork_controller.go	2	83.33%
pkg/state/state_ipoib_network.go	4	75.24%

Totals
Change from base Build 19683386909:	0.2%
Covered Lines:	4159
Relevant Lines:	6682

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💛 - Coveralls