postgres_fdw: add missing test files and fix regression tests

[roseduan]

Some essential files such as postgres_setup.bash and *_postgres_init.sql were missing, causing postgres_fdw regression tests to fail. These files existed in upstream GPDB. We restored them and fixed the tests so that all cases now pass.

Fixes #ISSUE_Number

What does this PR do?

Type of Change

• [ ] Bug fix (non-breaking change)
• [ ] New feature (non-breaking change)
• [ ] Breaking change (fix or feature with breaking changes)
• [ ] Documentation update

Breaking Changes

Test Plan

• [ ] Unit tests added/updated
• [ ] Integration tests added/updated
• [ ] Passed make installcheck
• [ ] Passed make -C src/test installcheck-cbdb-parallel

Impact

Performance:

User-facing changes:

Dependencies:

Checklist

• [ ] Followed contribution guide
• [ ] Added/updated documentation
• [ ] Reviewed code for security implications
• [ ] Requested review from cloudberry committers

Additional Context

CI Skip Instructions

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[my-ship-it]

Thanks for adding those tests back

[my-ship-it]

Add running tests to regular CI so that we can protect it?

[roseduan]

Add running tests to regular CI so that we can protect it?

Can we add postgres_fdw to our CI ? @edespino