fix: change stretch image in favor of buster to fix libpq < 10

[elhmn]

This pull request changes stretch based images to buster

Why ? The containers where not able to apply migrations correctly in postgres containers due, because the containers libpq were using a version < 10. You can find out more on this pull request https://github.com/PostgREST/postgrest/issues/1443

How ? It changes the stretch images to buster in the docker-compose.yml and docker-compose.test.yml files As it is done in this pull request https://github.com/PostgREST/postgrest/pull/1467

Steps to verify: Run make docker-e2etest if it runs without crashing it is alright