Fix volume path for PostgreSQL in docker-compose

[sudip-ibm]

Summary

Changes the mount path for postgres to work with postgres:18 Ref: https://github.com/docker-library/postgres/pull/1259

Checklist

• [ ] The Pull Request has tests
• [ ] A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• [ ] There is a user-facing docs PR against https://github.com/Kong/developer.konghq.com - PUT DOCS PR HERE

Issue reference

Fix #[issue number]