Update to containerd v1.7 series

[mboersma]

Describe the solution you'd like

CAPI images should be built with containerd v1.7.3 or later.

Describe alternatives you've considered

We could stick with the v1.6.x series longer, but:

This release [v1.7.0] is the last major release of containerd 1.x before 2.0.

Additional context

See #1241 (comment)

This is obviously a core dependency for images that support Kubernetes, so we have been cautious when updating it.
There aren't any breaking changes specifically called out in the containerd v1.7.0 release notes, but it's difficult to know what runtime bugs may appear since environments differ and we don't test the entire set of images that image-builder can produce.

Probably the best approach is try it and to leave the PR open long enough to gain as much feedback and testing as possible.

We should do an image-builder release before containerd v1.7 lands, just to be safe.

/kind feature