Fix Nextcloud and Postgres Docker Issue

I am seeking an expert to resolve an issue I'm experiencing with my Nextcloud and Postgres setup in Docker. The error occurs during the database initialization process. The error message reads: SQLSTATE[42501]: Insufficient privilege: 7 ERROR: permission denied for table oc_migrations.

I have already attempted some troubleshooting, specifically checking user permissions, but the problem persists.

Ideal Skills:
- Proficiency in Docker, Nextcloud, and Postgres
- Strong ability in troubleshooting database issues
- Experience in managing user permissions in Postgres

Please provide your strategy for diagnosing and fixing the issue in your proposal.