ref(build): build all images with buildx

[nojnhuh]

Description:
This change standardizes how all Docker images are built using buildx
to enable multi-platform images. OSM control plane images will be built
for linux/amd64 and linux/arm64. Demo images will be built for
linux/amd64 and windows/amd64.

There are no user-facing breaking changes, but dev workflows to build
images are slightly different. The biggest changes are that Go binaries
are built inside Docker instead of the native environment, and the
docker-push-* Makefile targets have been removed. See the dev guide
changes for more details.

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For reviewers

This is a big PR, but the "entrypoint" is the Makefile, so that's where I would suggest looking first, then the changes to the Dockerfiles. Everything else is mostly collateral damage from those changes.

Testing done:

I tested the main CI workflow on my fork: https://github.com/nojnhuh/osm/actions/runs/1593840436

I also created a release on my fork to test the release process and artifacts. Images are pushed to my docker hub (nojnhuh) with the tag v0.0.0-multiarchtest.0. I did osm install --set osm.image.registry=nojnhuh and spun up a bookbuyer pod to test pulling/starting the init container and that worked for me.

I have not tested the functionality of the windows/amd64 demo images or the linux/arm64 OSM images. If anyone has a cluster running with nodes that can run those, feedback would be appreciated.

Affected area:

Functional Area
New Functionality	[ ]
CI System	[X]
CLI Tool	[ ]
Certificate Management	[ ]
Control Plane	[ ]
Demo	[X]
Documentation	[ ]
Egress	[ ]
Ingress	[ ]
Install	[ ]
Networking	[ ]
Observability	[ ]
Performance	[ ]
SMI Policy	[ ]
Security	[ ]
Sidecar Injection	[ ]
Tests	[ ]
Upgrade	[ ]
Other	[ ]

Please answer the following questions with yes/no.

1. Does this change contain code from or inspired by another project? No

   • Did you notify the maintainers and provide attribution?

2. Is this a breaking change? Makefile targets to build images have been modified, but no user-facing breaking changes.

[codecov-commenter]

Codecov Report

Merging #4402 (67a5e16) into main (89b5661) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #4402   +/-   ##
=======================================
  Coverage   69.21%   69.21%           
=======================================
  Files         212      212           
  Lines       14580    14580           
=======================================
  Hits        10092    10092           
  Misses       4436     4436           
  Partials       52       52           

Flag	Coverage Δ
unittests	69.21% <ø> (ø)

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