Add Django database migrations to Dockerfile entrypoint

[AetherUnbound]

Fixes

Fixes #1048 by @AetherUnbound

Description

This PR adds the Django database migration to the Dockerfile entrypoint so it occurs automatically on startup. This can be disabled by setting DJANGO_MIGRATE_DB_ON_STARTUP=False.

Note
We'll want to add the disable flag to the current EC2-based deployment setup, since all of the instances in the auto-scaling group start at the same time which we want to avoid (see https://github.com/WordPress/openverse-infrastructure/issues/176).

Testing Instructions

1. Run just build && just up && just logs web and check that the "Running database migrations..." line does not show up in the logs.
2. Comment out the DJANGO_MIGRATE_DB_ON_STARTUP line in api/env.docker then run just up && just logs web and check that the "Running database migrations..." line does show up in the logs.
3. (Optional) Run just dj migrate api 0050 to roll back a migration. Then run just down && just up && just logs web and check that the migration is run automatically.

Checklist

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  Update index.md).
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• I added or updated tests for the changes I made (if applicable).
• I added or updated documentation (if applicable).
• I tried running the project locally and verified that there are no visible
  errors.

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[github-actions]

API Developer Docs Preview: Ready

https://wordpress.github.io/openverse-api/_preview/1049

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[sarayourfriend]

LGTM, though, what is the reason to disable this currently? I believe it would make applying the migrations in the current deployment easier as well (no need to manually connect the app locally, etc). In what cases do we absolutely need to disable the migrations running on startup?

For what it's worth, they run very fast when it's a no-op, so it wouldn't affect local development in any noticeable way.

[AetherUnbound]

My only concern about enabling this now is that we could see some undesired behavior if all 5 instances within the autoscaling group run the migration at the same time (this was a piece I mentioned in the original discussion too). I'm not aware of a way to have the ASG start up one instance at a time and verify that it's healthy, but I haven't looked in depth at how that could work. So in order to prevent concurrent migrations, I thought it best to disable this for the time being.

[sarayourfriend]

Oh, I see. I misremembered what you'd described the ASG deployment process was and thought that the ASG did deploy one at a time, but of course it does not 👍 This makes sense to me then.

[stacimc]

Tests well for me 👍