fixed postgres host for docker airflow setup

[neel-astro]

Description

Changes:

• Moved the default value for postgres.host back to postgres
• Pointed postgres host in webserver & scheduler of Podman containers to localhost, as there is no need for postgres.host since all containers run in the same pod.

🎟 Issue(s)

Related astronomer/issues#3929

🧪 Functional Testing

List the functional testing steps to confirm this feature or fix.

📸 Screenshots

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📋 Checklist

• Rebased from the main (or release if patching) branch (before testing)
• Ran make test before taking out of draft
• Added/updated applicable tests
• Tested against Houston-API and Astronomer (if necessary).
• Communicated to/tagged owners of respective clients potentially impacted by these changes.
• Updated any related documentation