Add arm64, ppc64el and s390x and migrate workflows to charm-ci

[weiiwang01]

What this PR does

Add arm64, ppc64el and s390x and migrate workflows to charm-ci.

Why we need it

Fix: #97

Migrating workflows to charm-ci is required for the multi-arch build.

Checklist

• I followed the contributing guide
• I added or updated the documentation (if applicable)
• I updated docs/changelog.md with user-relevant changes
• I used AI to assist with preparing this PR
• I added or updated tests as needed (unit and integration)
• If integration test modules are used: I updated the workflow configuration
  (e.g., in .github/workflows/integration_tests.yaml, ensure the modules list is correct)
• If this is a Grafana dashboard: I added a screenshot of the dashboard
• If this is Terraform: terraform fmt passes and tflint reports no errors
• If this is Rockcraft: I updated the version

[florentianayuwono]

did this run the tests for 20.04 and 22.04? somehow i couldn't see the checks for these bases (only 24.04 is present)

[weiiwang01]

did this run the tests for 20.04 and 22.04? somehow i couldn't see the checks for these bases (only 24.04 is present)

Yes, the 24.04 in the test name (for example, integration-test / integration-test-ci:ubuntu-24.04-arm64:build/tests/integration/run:focal) refers to the test runner name. And the base variant is at the end of the name (focal). You can see this test is running with the base 20.04 in the test argument.

https://github.com/canonical/aproxy-operator/actions/runs/28387227288/job/84105129726#step:11:1150

[florentianayuwono]

lgtm thanks weii!