Modify deployment steps to wait for new migrations to finish before deploying new app versions

[exalate-issue-sync]

Original spike ticket: https://fecgov.atlassian.net/browse/FECFILE-1773

Diagram: https://docs.google.com/drawings/d/1HNd2piLJSSuYqqNbh_yGCTRyQFbEwOU2PSU4yX0QM_I/edit


1. Migrations could be run by an app without a route
2. Migrations should completely finish before new application versions are deployed
3. Should probably modify the deploy task itself in (tasks.py). See https://github.com/fecgov/openFEC/blob/99b62ee48ac31fc352aaa287cc4304533c8328b2/tasks.py#L185-L212 for an example (flask/flyway but some of the basic principles are the same)
4. Could possibly reuse deployer instance with no routes as a non-deployer instance after migrations (add route to the application instance afterwards)
5. Take manage.py migrate out of the existing run-api.sh
6. Test partially failed migrations / rollback

QA Notes

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DEV Notes

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Design

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See full ticket and images here: FECFILE-1865