Pin Postgres Docker image to stable version instead of using latest tag

[coderabbitai]

Description

Currently, the Docker Compose configuration uses postgres:latest which can introduce breaking changes without warning when major version upgrades occur.

Current State

image: postgres:latest

Desired State

Pin to a specific major/minor version to ensure consistent and repeatable environments:

image: postgres:16-alpine  # or postgres:15

Benefits

• Prevents unexpected breaking changes from major version upgrades
• Ensures consistent behavior across local development and CI environments
• Provides predictable and repeatable deployments

Reference

• PR: fix: update retry policy to unless-stopped for all docker-compose services #435
• Comment: fix: update retry policy to unless-stopped for all docker-compose services #435 (comment)
• Requested by: @kshitij-k-osmosys