chore: switch to ECR Public from Docker Hub

[weihanglo]

What does this PR try to resolve?

We're hitting this hard.

[internal] load metadata for docker.io/library/httpd:2.4-alpine
ERROR: failed to copy: httpReadSeeker:
failed open: unexpected status code https://registry-1.docker.io/v2/library/httpd/manifests/sha256:66c49302c02430619abb84240a438bcfc083015661009fcaaeaac931450f62cd:
  429 Too Many Requests - Server message: toomanyrequests:
You have reached your pull rate limit.
You may increase the limit by authenticating and upgrading:
https://www.docker.com/increase-rate-limit

And the rate limit seems quite easy to hit.

The rate limits of 100 container image requests per six hours for
anonymous usage, > and 200 container image requests per six hours
for free Docker accounts are now in effect. Image requests exceeding
these limits will be denied until the six hour window elapses.

This PR switches to Amazon ECR public, and alternative image registry,
to unblock us from the rate limit of the official Docker registry.

Both of the two images are verified and uploaded by Docker

• https://gallery.ecr.aws/docker/library/alpine
• https://gallery.ecr.aws/docker/library/httpd

See also https://gallery.ecr.aws/

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[sourcefrog]

Just a thought: arguably we should switch to Azure's registry instead, since GitHub workers probably run on Azure? (I'm not totally sure they have public mirrors of this but it seems like they would?)

[sourcefrog]

.. In a bit of searching I can't find public mirrors like this on Azure.

Within GH itself, there is https://github.com/linuxcontainers/alpine/pkgs/container/alpine but I don't think this includes Apache and I'm not sure it should be equally trusted.

[weihanglo]

Seems like we have recovered from the rate limit: #14682 (comment). I am fine with either closing or merging this.

[weihanglo]

.. In a bit of searching I can't find public mirrors like this on Azure.

Neither can I find Azure equivalent. And nothing in https://github.com/orgs/apache/packages nor https://github.com/orgs/alpinelinux/packages 😞.

[ehuss]

I opened rust-lang/infra-team#176 to figure out what we should do here.

[weihanglo]

Going to close in favor of the discussion rust-lang/infra-team#176.