fix(run/django): Update to Procfile, Artifact Registry, dedicated service account

[glasnt]

Description

Fixes b/364075989, cl/688789319

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Checklist

• I have followed Sample Guidelines from AUTHORING_GUIDE.MD
• README is updated to include all relevant information
• Tests pass: nox -s py-3.9 (see Test Environment Setup)
• Lint pass: nox -s lint (see Test Environment Setup)
• These samples need a new API enabled in testing projects to pass (let us know which ones)
• These samples need a new/updated env vars in testing projects set to pass (let us know which ones)
• This sample adds a new sample directory, and I updated the CODEOWNERS file with the codeowners for this sample
• This sample adds a new Product API, and I updated the Blunderbuss issue/PR auto-assigner with the codeowners for this sample
• Please merge this PR for me once it is approved

[snippet-bot]

Here is the summary of changes.

You are about to add 2 region tags.

• run/django/Procfile:4, tag cloudrun_django_procfile_migrate
• run/django/Procfile:9, tag cloudrun_django_procfile_superuser

You are about to delete 1 region tag.

• run/django/mysite/migrations/0001_createsuperuser.py:15, tag cloudrun_django_superuser

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[glasnt]

Blocked on cl/691542544 to pin region tag that is being deprecated.

[glasnt]

I can't seem to re-run snippetbot here :(

Update: Oh there it goes!

[iennae]

this look like it's deprecated/unsupported

[glasnt]

It's the one currently listed on https://cloud.google.com/docs/buildpacks/build-application#build_an_application_remotely

If that changes, we should promptly update all samples that uses the old image.

[glasnt]

I can try the (probable) replacement "buildpacksio/pack", as this seems to work in isolation.

[iennae]

This looks good to me. Thanks for the thorough update.